Kill switch wiring

[JoshS]

I did a couple of searches on this forum and elsewhere, and found some good discussions, but really couldn't convince myself of the right thing, and I'm no electrical engineer. I'm a visually-oriented guy, so maybe using these diagrams you can all help me.

Given the wiring diagram below, can I place a simple single-pole switch in the circuit that runs around the left and top of the diagram, either right before or right after the big 200A fuse? Or do I need one of the multi-pole switches that somehow connect into the alternator circuit?

I'm thinking the simpler approach will work. The junction point with the 8 large fuses you see eventually leads to the ignition switch, among other places.

http://members.roadfly.com/jsirota/Z3Coupe/WiringDiagram-e36z3_99.jpg

If I need the multi-pole switch, can someone please explain to me how to wire it? I found this diagram below from Pegasus, but it's not descriptive enough for me to know what to do with it. Pegasus seems to say that all cars with alternators need these multi-pole switches, but based on what I've read elsewhere, as long as the alternator is still connected to the battery, then the single-pole switch should work?

http://www.pegasusautoracing.com/Images/L/4430-inst.jpg

Thanks for the help!

[JimLill]

Keep in mind that the kill switch must not only stop the engine but should isolate vehicle wiring from the battery to minimize a fire threat. The Red connection in my diagram when wired as shown, does just that. I lack enough time to give you more detail, but that Pegasus sourced diagram is concise and correct, may just be some hlepful hints for a electro-newbie!

this may help people explain it.......

http://www.vectorbd.com/r-series/4430-inst.jpg

In answer to the multi-pole switch comment. The Pegasus is 3PST 2 poles are NO and 1 pole is NC.

The Red/Green and Violet/Yellow are N.O. and the Blue/Orange is N.C.

[JimLill]

putting any electric fuel pump on the feed with the ignition coil is a good idea too.

When you throw the Kill switch to OFF, here's what happens:

1 - the battery is obviously otally disconnected
2 - the ignition and fuel shut down
3 - the alternator gets a small load to protect its diodes etc.

[JoshS]

My confusion about the Pegasus diagram is that there is no simple wire from the ignition switch to the coil in my car. My car has all sorts of fancy electronics, six ignition coils, an electronic anti-theft immobilizer, a multi-pole ignition switch with several wires on the output side, etc.

It's just not obvious what wire to disconnect to shut the car off. I was hoping that the simpler thing would in fact kill the engine, based on, among other things, this thread (http://itforum.improvedtouring.com/forums/index.php?showtopic=4586).

[JimLill]

My confusion about the Pegasus diagram is that there is no simple wire from the ignition switch to the coil in my car. [/b]

Locate the group of wires that connect to the "run" position on your ignition switch, route that group through the kill switch "ignition" path.

[Greg Amy]

If you isolate the battery with the main circuit, and run the alternator field circuit through the normally-open circuit with the resistor, you'll be fine.

The resistor circuit is there primarily to protect the contacts of the main circuit (and really should be used on any car, regardless of what charging system you have). If you simply open up such a high-current circuit as the battery, that load has to go somewhere; without the resistor circuit it arcs the contacts of the main switch. Giving the load someplace to slowly drain protects those contacts.

Further, if the field circuit of an alternator stays energized (as it can with a charning system) then it can harm the alternator.

So, by running the field circuit of the alternator through the NO circuit with resistor, you resolve both problems.

As far as Tech is concerned, if they can reach over and shut off your car entirely with that switch (and trust me, they'll test it) then it's fine. They/we don't give two shakes what it does to the components of the charnging system; their concern is safety, your concern is making sure it doesn't hurt stuff...

[JoshS]

Locate the group of wires that connect to the "run" position on your ignition switch, route that group through the kill switch "ignition" path.
[/b]

I'm sure I could find the right thing. There is a wire at the coil packs that feeds all six, I could probably pick it up there instead of at the switch. At the switch, there is a line that's hot in run, and a line that's hot in both run & start. Seems like to kill the ignition it would be the second one. Or I could get them at the coils.

Between the switch and the coils is so much electronics that you really can't tell what's going on.

But ... what I really want to know is, will the first approach work? It seems like it. The alternator output side (the B+ terminal) would be connected directly to the battery, even when the switch is off, so it would have somewhere to drain. However, with the switch off, there would be no contact between the battery/alternator and the ignition. Isn't this simple approach the best approach?



If you isolate the battery with the main circuit, and run the alternator field circuit through the normally-open circuit with the resistor, you'll be fine.
[/b]
Forgive me Greg ... I don't understand a word you just said! I don't know what a field circuit is, and I don't really understand what you mean by "main circuit" either.

Can you draw me a picture?

I understand the principle of protecting things with the resistor ... I just don't understand why the first approach doesn't do that.

[Greg Amy]

I don't really understand what you mean by "main circuit"...[/b]
The main circuit from the battery to the car, just as in the drawings above.


I don't know what a field circuit is...[/b]
VERY basically put, alternators work on the concept of comparing a circuit in the car to what voltage it's putting out, always trying to keep them equal to its setting. In the case of a 12V car, that's about 13.5 volts. If that secondary circuit, the field circuit, gets low on voltage the alternator puts out more; if it gets high, less.

Therefore, with an alternator, if you cut off the battery only then as the field circuit voltage drops the alternator tries to out out more and more voltage. Eventually the field circuit voltage will drops too low and the alternator goes offline, but it's not instantaneous, and in the interim the alternator continues trying to charge pu the system to ~13.5V.

However, if you open this field circuit with a switch or relay then the alternator sees zero voltage and drops offline.

So, you can wire the car one of two ways: wire the kill switch's smaller secondary contacts such that it disconnects the field circuit and the alternator goes offline, system voltage drops to zero, and the car quits running due to lack of electrical power; or, you can wire the ignition through those secondary contacts so the car quits running and the alternaotr stops producing power due to lack of rotation.

Either way works fine, simply choose the method that is most convenient for your car and kill switch location. - GA

[JoshS]

VERY basically put, alternators work on the concept of comparing a circuit in the car to what voltage it's putting out, always trying to keep them equal to its setting. In the case of a 12V car, that's about 13.5 volts. If that secondary circuit, the field circuit, gets low on voltage the alternator puts out more; if it gets high, less.

Therefore, with an alternator, if you cut off the battery only then as the field circuit voltage drops the alternator tries to out out more and more voltage. Eventually the field circuit voltage will drops too low and the alternator goes offline, but it's not instantaneous, and in the interim the alternator continues trying to charge pu the system to ~13.5V.
[/b]
Thanks! I get it. The point of the secondary kill circuit is to reduce the amount of time it takes to get the alternator fully off-line.

Now, just out of curiosity, what harm is caused during this duration of time if the alternator main circuit is still connected to the battery, as my original question asked?

[JimLill]

My confusion about the Pegasus diagram is that there is no simple wire from the ignition switch to the coil in my car. [/b]

Locate the group of wires that connect to the "run" position on your ignition switch, route that group through the kill switch "ignition" path.

2nd post by accident...... how to delete??

[JoshS]

Locate the group of wires that connect to the "run" position on your ignition switch, route that group through the kill switch "ignition" path.
[/b]
Yeah, there is no "run" terminal of the switch. There is one terminal hot in acc/run/start, and another that's hot in run/start. (There are others too, but those are the ones used that are hot in run). The point is that there are two of them, and the switches on the market have only one.

I still don't get why the simpler approach won't work or could cause any harm.

[Greg Amy]

...what harm is caused during this duration of time if the alternator main circuit is still connected to the battery, as my original question asked?[/b]

The "generally accepted" problem is one of damage to the alternator; alternators REALLY WANT to have some kind of accumulator to dampen the positive and negative spikes it produces, and that's the battery's job. You disconnect that battery from the equation and you run the risk of alternator damage or possibly runaway.

"Runaway"? From a safety aspect, theoretically an alternator-equipped car can continue to run with the battery disconnected. The car will run as long as the electrical system has voltage; the alternator will continue to put out voltage as long as the field circuit is "excited"; the field circuit will remain "excited" as long as the alternator is putting out voltage. See the Catch-22 there?

I've never tried shutting of my car with the kill switch without the alternator/ignition properly wired, so I can't say that's what will happen for sure. But I certainly don't want to try it on my car. Maybe this is a good one for Mythbusters?

The goal is to get the car to stop running, with all electrical equipment de-energized. You'll do that either by stopping the alternator from turning (by shutting off the ignition) or getting the alternator to stop putting out electricity by opening the field circuit (thus killing the ignition due to lack of electricity). Either way works.

I can assure you that, upon presenting your car to an SCCA tech inspector for its logbook, one of the very first things the inspector will do is ask you to start the car then he/she will reach over and flip off the master kill switch to see if the car stops. If you're comfortable having someone do this using just the battery circuit, and it works, then you're all set... - GA

[JoshS]

I can assure you that, upon presenting your car to an SCCA tech inspector for its logbook, one of the very first things the inspector will do is ask you to start the car then he/she will reach over and flip off the master kill switch to see if the car stops. If you're comfortable having someone do this using just the battery circuit, and it works, then you're all set... - GA
[/b]
I understand that. But somehow we're not understanding each other. It's probably me because I didn't stay at a Holiday Inn Express last night.

Based on the diagram in teh first post, the car is wired such that the positive connection of the battery has two leads, one which connects to the alternator (let's call it "wire 1") and one which connects to the ignition system and the rest of the car's electrics ("wire 2").

If the car is running, and the alternator is producing output, that output will be going straight to the battery on wire 1, and then from the battery to the ignition system on wire 2.

If I put a switch in the middle of wire 2, then when that circuit is broken, there will be no voltage on the field circuit, either from the battery or from the alternator, because both the alternator and the battery are upstream of the switch. Further, the alternator isn't left hanging with nothing to absorb its remaining energy, because it can still reach the battery on wire 1. Seems to solve all of the problems. And yet I keep reading between the lines of what you are saying, in which you are implying that either this will not stop the engine, or maybe you're saying that it will stop the engine but will harm the car's alternator or other systems.

What the heck am I missing?

[Greg Amy]

What the heck am I missing?[/b]

GCR 17.27: "The master switch shall be installed directly in either battery cable and shall cut all electrical circuits..." (my emphasis) I was describing above with this requirement as an assumption.

You don't have a choice: the battery must be completely isolated from the rest of electrical system. If you did it as you describe, then the remainder of the car's electrical system is still getting juice from the battery.

Remember: it's not JUST about getting the car to shut off; it's about getting the car to shut off AND have no charge to ANYTHING else in the car. Picture running fuel pumps while you're upside down, or battery cables chafing against smashed sheet metal with dripping fuel, or sparking instrument cluster wires 2 feet from your fasce, and so forth.

You will have to remove those two wires from the battery, attach them to a common block, run a cable from that block to the kill switch (or run the two wires on ring terminals to one side of the switch), then from there to the battery. Alternately, you can bisect the battery ground wire with the kill switch. THEN, you run either the ignition or alternator field circuit through the smaller terminals, and now you're golden.

[JoshS]

GCR 17.27: "The master switch shall be installed directly in either battery cable and shall cut all electrical circuits..." (my emphasis) I was describing above with this requirement as an assumption.
[/b]
Good point, okay, now we're done. What that also means is that the other thread from this forum that I referred to earlier was giving bad advice, as it recommended connecting the alternator directly to the battery.

So thanks. Sorry that it took us so long to get there.

[Greg Amy]

Really, not a problem. Good mental exercise for all of us... - GA

[DavidM]

"Runaway"? From a safety aspect, theoretically an alternator-equipped car can continue to run with the battery disconnected. The car will run as long as the electrical system has voltage; the alternator will continue to put out voltage as long as the field circuit is "excited"; the field circuit will remain "excited" as long as the alternator is putting out voltage. See the Catch-22 there?

I've never tried shutting of my car with the kill switch without the alternator/ignition properly wired, so I can't say that's what will happen for sure. But I certainly don't want to try it on my car. Maybe this is a good one for Mythbusters?
[/b]

The car keeps running. My car had a single pole switch on it when I got it that just disconnected the battery from the car. I didn't know any better at that point. I go to my first ever annual tech and the first thing the inspector does is throw the kill switch. The car keeps on running. My comment was "It's not supposed to do that is it." I have no idea how Bob passed annual. I replaced it with a three pole switch that disconnects the computer signal to the ignition coil. The car now stops. Moral of the story: You need something other than just disconnecting the battery from the car.

David

[pfcs49]

GUYS! keep this simple AND reliable. Let the kill swx main posts disconnect the battery.
Let one loww current kill swx ground the grounded leg of the ignition coil, killing the engine but leaving all run consumers (fuelpump, etc) to load the alt as it coasts to a stop. (if you don't have a single coil, then put both legs of the low current circuit across the crank sensor, etc.
Not only is this a very simple circuit, but it fails safe in regard to cutting out the engine in competition-if the low current switch gets resistive/corroded, it doesn't effect running, just killing. Phil

[Z3_GoCar]

The car keeps running. My car had a single pole switch on it when I got it that just disconnected the battery from the car. I didn't know any better at that point. I go to my first ever annual tech and the first thing the inspector does is throw the kill switch. The car keeps on running. My comment was "It's not supposed to do that is it." I have no idea how Bob passed annual. I replaced it with a three pole switch that disconnects the computer signal to the ignition coil. The car now stops. Moral of the story: You need something other than just disconnecting the battery from the car.

David
[/b]

Josh,

You'll want to wire the two pole switch to the two wires that run from the battery to the engine compartment on the passenger side. There should be an ignition relay in your circuit, I don't have the Bently manual in front of me right now, but I do remember it being there, it's in the immobilizer part of the curcuit. Anyway, the problem is that the switch just removes the 12v. it really needs to ground out the alternator and computer, to make the circuit dead, this is what the relay does ground the curcit when it's off, applies 12v. when it's on. This is where the alternator feedback can keep the motor running with the battery disconnected when there's no path to drop the voltage in the field wire. I wired the Battery Cutoff Switch (BCS) in series with a toggle switch on the small wire, this energises the relay and ungrounds the alternator field, computer key switch wire, and fuel pump wire. This way the BCS and the toggle both kill the motor, but the BCS removes all electricity from going into the engine bay. I can tell you the wire numbers you want to look for and the colors if you like, but the BCS should be along the main battery wire running along the passenger side. Good luck,

James

[Z3_GoCar]

GCR 17.27: "The master switch shall be installed directly in either battery cable and shall cut all electrical circuits..." (my emphasis) I was describing above with this requirement as an assumption.

You don't have a choice: the battery must be completely isolated from the rest of electrical system. If you did it as you describe, then the remainder of the car's electrical system is still getting juice from the battery.

....

[/b]

Greg,

Though I'd mention one exception which is electrically actuated fire systems must be hot at all times even when the BCS is off. If it's a pull cable like mine then all dead is good.

James

[raffaelli]

Can the lines which pass through the fire wall be continuous or do they need to be interrupted by one of those bulkhead terminals? I poked around a bit but could not find the answer. Should the line be continuous, what is commonly used to seal the opening?

[joeg]

A properly sized rubber grommet.

[Greg Amy]

Can the lines which pass through the fire wall be continuous or do they need to be interrupted by one of those bulkhead terminals?
AFAIK, there is no regulation in regards to that. Use your best judgment and best practices. - GA

[raffaelli]

I am suprised that the rules are not more clear on what the requirements are.

I see on the Summit site some pretty neat grommets. But....$18 each??????? :eek::eek::eek:
http://static.summitracing.com/global/images/prod/large/sit-gs1003-12_grp.jpg





I think I will stick with the $10 assortment pack.

[wepsbee]

GUYS! keep this simple AND reliable. Let the kill swx main posts disconnect the battery.
Let one loww current kill swx ground the grounded leg of the ignition coil, killing the engine but leaving all run consumers (fuelpump, etc) to load the alt as it coasts to a stop. (if you don't have a single coil, then put both legs of the low current circuit across the crank sensor, etc.
Not only is this a very simple circuit, but it fails safe in regard to cutting out the engine in competition-if the low current switch gets resistive/corroded, it doesn't effect running, just killing. Phil


Does anyone know if this simple circuit will do any harm to the MSD ignition system??

[raffaelli]

Hey fellas. Can you check me on my wiring before I apply power? The sketch is attached.

[group7]

Does anyone know if this simple circuit will do any harm to the MSD ignition system??
I just spoke to MSD tech line with the same question, they recommended wiring the power feed to the box (heavy red wire) through the secondary contacts of the switch but switching switched power wire (smaller red would be acceptable. No damage to box with either according to their tech guy.
Daryl E.

[wepsbee]

I just spoke to MSD tech line with the same question, they recommended wiring the power feed to the box (heavy red wire) through the secondary contacts of the switch but switching switched power wire (smaller red would be acceptable. No damage to box with either according to their tech guy.
Daryl E.

Thanks for checking!!

[Joe Foering]

Greg, is this relevant to a dodge charger? Should I get a kill switch with the 6 terminals (2 lge, 4 sm)?

[Greg Amy]

Greg, is this relevant to a dodge charger? Should I get a kill switch with the 6 terminals (2 lge, 4 sm)?
Yes, it's relevant to all cars with alternators. I strongly recommend the 6-pole kill switch, with the two large terminals for the battery circuit, the normally-open (NO) circuit for the bleed resistor, and the normally-closed (NC) circuit for the ignition circuit... - GA

[chuck baader]

Quick and dirty way....red battery wire to switch. Jumper from red wire to one side of aux switch. Other side of main switch to starter, etc. Other side of aux switch to wire going to feed fuse box. Done. Start and stop car with key...charge battery...kill everything with kill switch. Chuck

[Greg Amy]

...kill everything with kill switch.
And, possibly, your alternator diodes and some electronic components as well due to the surge...that's what the resistor bleed circuit is for: to slowly bleed down all potential energy (voltage), rather than simply shutting the door in its face...

All that voltage gotta go somewhere, and if the battery isn't there to absorb the shock (its secondary purpose is to dampen voltage spikes and act as an electrical accumulator) then something will... - GA

[chuck baader]

Greg, not to be argumentative, but I have wired 5 e30 BMWs that way with no issues. The only problems with the BMWs is when you remove the cluster..you must add a bocking diode to the circuit to replace the one removed from the alternator light. Chuck

[cjb25hs]

What size wire do I need to use?

[Flyinglizard]

You could break the negative side. WFM. MM

[Streetwise guy]

Just to make life a bit more interesting, most Bosch alternators are internally regulated, and will continue to charge unless you disconnect the main power feed, which will have unpleasant effects on the alternator diodes. I have hooked my kill into the trigger circuit on the main efi relay (Dodge calls it the ASD relay), which on my Neon kills alternator field, ignition and injector pulse. The advantage to using a low amperage circuit like a relay trigger wire is there is no chance of burning up the kill switch. The disadvantage, as I discovered when I installed an unknown used kill switch, is that not only does the car quit charging if there is a problem, the injectors and ignition quit too.:018: Post up the wiring diagram of your cars injection relay, and I'll show ya which wire to cut.

[JimLill]

as for going through the fire wall......... make a hole the size that heater hose fits snugly through and use that for your cheap grommet, with the batt+ through the hose. $.25 fix

[Tristan Smith]

Ok, I am finally wiring up the 300zx. It's been 10 years since I wired up the 240sx, and I am embarrassed to say I have forgotten what I did exactly.

So I get the battery part. The secondary circuit will cut the alt. field wire where it circles back to the alternator, to disconnect the alt. circuit.



The only problems with the BMWs is when you remove the cluster..you must add a bocking diode to the circuit to replace the one removed from the alternator light. Chuck

Chuck, I will not have the cluster in the dash, so I would need to add a bocking (sp?) diode in addition to the Bulb Check Relay, which would just be grounded to slowly bleed off any surge or spike at the alternator. Correct?

Greg Amy, jump in on this.

Thanks.

[Greg Amy]

Tristan, I'm not familiar with "the BMW problem" and its systems, so I really can't speak to that. However, I consider that circuit with resistor for slowly bleeding electrical potential to ground pretty important (see first post, second diagram)... :shrug:

[keilysmith]

It can be as easy as simply adding a little child and a transient (normally open) switch. Look for the sign "hot" exhaust - is a cable that goes from the center of the leg volume control, and ends at the end "tab on the outlet. Now, add a cable, for example, during the volume control, and welding of this cable to switch (either legs up). Then another wire bond for the remaining leg (the two who want to use) the switch and solder the other end to ground.

[Flyinglizard]

If you break the neg side and break the fuel pump ground wire at the same time, the car shuts off, fuel flow stops , and the whole wire system has better crash resistance. Smashing the ground wire into bodywork wont start a fire. This also avoids the big hassle of the alt contining to run the car.
The Bosch alt are often self exciting/ firing at around 3200=4000rpm . Check yours. Most will start without a light/exciter wire. For the few that need a light , I use two side marker light sockets and bulbs. The diode is in the alt , glowing the bulbs, key on engine off. When the car/alt fires, the lights go out.
I use this method for the ministock that needs to make a vacuuum rule. I need the alt load to increase the vacuuum so that I can use more cam.
I use two bulbs, because if one burns out the alt will not fire and the car wont make vac, costing me a DQ and money..
FWIW, many race cars have the starter power bypassing the bat break. The break switch does not like the high amps for very long and often results in a no start on the grid with 2 to go.
I dont condone this wiring, but my endurance car has the bat switch that can be bypassed really quickly.
HTH, MM

[JohnRW]

It can be as easy as simply adding a little child and a transient (normally open) switch. Look for the sign "hot" exhaust - is a cable that goes from the center of the leg volume control, and ends at the end "tab on the outlet. Now, add a cable, for example, during the volume control, and welding of this cable to switch (either legs up). Then another wire bond for the remaining leg (the two who want to use) the switch and solder the other end to ground.


kielysmith = http://www.youtube.com/watch?v=G6D1YI-41ao

[Greg Amy]

As long as we're sullying the topic...I'll match your Hungarian with a Turbo Encabulator...

http://www.youtube.com/watch?v=rLDgQg6bq7o

...and raise you a Retro Encabulator.

http://www.youtube.com/watch?v=RXJKdh1KZ0w

(it's funny as hell when John and I think of the same things... ;) )

[tom91ita]

try looking at how i wired my 86ish honda crx.

http://www.flickr.com/photos/tom91ita/sets/72157603191663037/

basically, i tried to show on the car's wiring diagram and the switch wiring diagram how they relate to each other.

so connection "A" or "D" on the switch is shown as "A" or "D" on the wiring diagram.

hope this helps. btw, i have done the annual tests as well race weekend tests and never hurt the alternator. (weekend tests are wondering why the car won't start when i arrive at the track and then remembering i keep the master switch off in the trailer......)

[mossaidis]

Posting for a friend that is prepping his car for SCCA in NARRC ITE..

We're trying to wire the killswitch. He has a late 1.8T VW motor in a 84 Scriocco.

"The problem with the altenator is that it takes it's feed for the exciter wire directly from the battery cable wire from the back of the car. I will asssume I have to cut all power to the main feed cable before the altenator? Not sure how to isolate it completely from the system so the car shuts off when switched."

[Greg Amy]

How "late" of a VW 1.8t?

Most VWs use Bosch alternators with internal field circuitry; ergo not even with the sheisrocket would there be a field wire to bisect. In that case, I'd recommend bisecting the wire from the battery to the starter with the main cut off circuit, then bisecting the main ignition wire through the secondary normally open circuit of the switch ("Z or 2" in the diagram on page one.)

For the 1984 Scirocco, the secondary wire to bisect would be the "15" or "switch on" circuit that supplies power to the rest of the car, a 16-gauge black wire coming off the ignition switch. Cut that wire and the car dies.

GA

[GTIspirit]

I encountered similar situation on my '87 VW GTI 16V when wiring the kill switch. Alternator keeps the engine running quite fine when battery power is cut..... So I plan on interrupting the "T15" to the ignition because that will kill the spark which will in turn kill the fuel pump. Most vehicles should have some kind of fuel pump enable that's controlled by the ignition. So when the engine stops running the fuel pump stops pumping, no need for a separate fuel pump cut. This should also dissipate the charge from the alternator so there is no risk of blowing the regulator with a sudden shutoff of the alternator output.

[dhrmx5]

This is a subject that is a real pain to me. Yet another vaguely written rule in the GCR that is subject to interpretation.

I have always wired my switches to kill battery power and the fuel pump. Cars will run just with just a battery or an alternator but if you take away the fuel I guarantee the engine is going to die. Sure, it takes a few seconds for the engine to shut off and the alternator to lose it's energy but at that point in time ALL circuits are dead and there are no fuel lines pressurized to 60-90 psi just waiting to burn through or crack and cause a flash fire. Fuel pressure is gone because the engine burned it off. Certainly a much safer scenario for the turn worker who is trying to assist you or put out an underhood oil/gas fire.

Why is the rule poorly written? There are no criteria for time, testing, or wiring for most cars. The fact that the GCR is specific about wiring a SRF but not any other vehicle leads me to believe there are options as to how the results are accomplished. The way I wire my car has all circuits dead with the car running after a few seconds and the circuits are all dead with the car not running. Given that the rule simply states that all circuits must be cut would mean that my wiring accomplishes that goal.

[CRallo]

best first post ever?


This is a subject that is a real pain to me. Yet another vaguely written rule in the GCR that is subject to interpretation.

I have always wired my switches to kill battery power and the fuel pump. Cars will run just with just a battery or an alternator but if you take away the fuel I guarantee the engine is going to die. Sure, it takes a few seconds for the engine to shut off and the alternator to lose it's energy but at that point in time ALL circuits are dead and there are no fuel lines pressurized to 60-90 psi just waiting to burn through or crack and cause a flash fire. Fuel pressure is gone because the engine burned it off. Certainly a much safer scenario for the turn worker who is trying to assist you or put out an underhood oil/gas fire.

Why is the rule poorly written? There are no criteria for time, testing, or wiring for most cars. The fact that the GCR is specific about wiring a SRF but not any other vehicle leads me to believe there are options as to how the results are accomplished. The way I wire my car has all circuits dead with the car running after a few seconds and the circuits are all dead with the car not running. Given that the rule simply states that all circuits must be cut would mean that my wiring accomplishes that goal.

[Greg Amy]

Don't overthink it; it's all about safety.

Think of it this way: what if you were upside down in a Miata and the damn thing caught on fire, still running thus the alternator still juicing, and it was porking out fuel from a ruptured fuel line; what would YOU think about "just a few seconds" of additional chassis electricity after hitting the kill switch?

After all, what's "just a few seconds" of ruptured fuel line between friends?

That's the kind of stuff I think of when I'm tech'ing a car. If I tested your kill switch and it continued to run "just a few seconds" after I hit the switch, I'm dingin' ya, plain and simple. You can argue all the technicalities you want - and you'd be right, from a purely technical standpoint - but when you hit the kill switch the engine should stop, right then and there, with no power to anything at all, no delay, no dwell time, and certainly not within a few seconds.

And that's really the way it should be.

And when it comes down to it, how is splicing into the alternator field circuit wire (or the ignition circuit wire) any more difficult than splicing into the fuel pump wire? Just do it "correctly" and everyone's happy, yes? - GA

[Flyinglizard]

I wire all of the new builds to cut the fuel pump power. The modern car has so many relays, field wires, diodes, etc.
The only sure way to stop the fuel fire( and that is the reason for the power switch),is to drop the power to the fuel pump.
Remember Greg, AT idle the stop may be 2sec, at RPM the stop is right now.
Never had any issues at tech. Actually they like my cars, cuz they shut off.
MM
pS the VW does not need a field wire.. Most ,if not all, will self field @ about 3500rpm, engine speed.

[Z3_GoCar]

As long as the alternator self-energises any thing, all circuits are not dead. I ground out the ecu key wire, the alternator field wire, and the fuel pump wire, with a immobilizer relay. Imagine that, I use a relay that's already in the wiring, and on the car.

The rule flexibility is because not every car has a coil wire, or it may be a fuel cut-off valve on a carburetor, or in my case it's the ecu wire. Some cars didn't come from the factory with an immobilizer relay, but they're easy to get from your local alarm/sterio shop.

[Matt93SE]

Quick and dirty method:
wire the alternator output to the battery side of the cutoff switch. no need to fiddle with field wires, ECUs, fuel pump relays, nothing.

when you flip the switch, there is ZERO power anywhere under the hood. Zip. Zilch. Nada. No fuel pump, no ignition, no ECU. Absolutely foolproof and there's no freewheeling alternator feeding back into the circuit to fry the ECU.

Even if the alternator is self-fielding, all it's doing is charging the battery that is already disconnected. Took me about 6' of #8 wire and 30 min to accomplish the job.

[JoshS]

Quick and dirty method:
wire the alternator output to the battery side of the cutoff switch. no need to fiddle with field wires, ECUs, fuel pump relays, nothing.

when you flip the switch, there is ZERO power anywhere under the hood. Zip. Zilch. Nada.

Uhh ... except for that big wire going to the alternator ... Doesn't cut "all circuits."

[Flyinglizard]

That is the only way to do it with a 2 post switch. It is the common way, not the ideal way but it is done.

[Matt93SE]

Uhh ... except for that big wire going to the alternator ... Doesn't cut "all circuits."
since the field coils on the alternator are cut, it effectively cuts "all circuits". All sources of power are on one side of the switch, all users of power are on the other. You flip the switch and the car stops. right now. What else do you want?

[JoshS]

since the field coils on the alternator are cut, it effectively cuts "all circuits". All sources of power are on one side of the switch, all users of power are on the other. You flip the switch and the car stops. right now. What else do you want?

Maybe that's good enough, and as I think about it, maybe I'm colored by the fact that my car has its battery in the back. I was trying to avoid having any electricity in the engine compartment. But I suppose if the battery is in the engine compartment, that's not a realistic goal.

But it says "all circuits" and as long as there's a circuit from the battery to the alternator, to the engine ground, back to the battery, it's hard to argue that it meets the letter of the rule.

[Matt93SE]

My battery is in the trunk as well. the only wire that's hot going into the engine compartment is the short wire going to the alternator. If you're in a wreck big enough to rip the alternator off its mount or break the engine loose, then a little #8 cable is the least of your worries.
As for cutting all circuits, I would implore you to argue that one to tech. this method cuts anything and everything that uses power or could keep the engine running. there is ONE wire going into the engine bay that's still got juice on it, and it's not going anywhere that's going to keep the car running. That's the intent of the rule, is it not?

[Simon T.]

Well silly me waited until the week of the ARRC to figure out my kill switch, I THOUGHT it was going to be easy but underestimated it. I made a switch panel a while back from my ignition switch and thought I could combine that wiring (the switch that kills pump and what not) to my battery kill switch and be golden, sadly I was wrong.

I have a two terminal switch. I see people use ones with 4 and 6 sometimes, so is there anyway to do it with just two?

If I wire my hot alternator wire directly to my battery then run that cable to one side of the switch and run the other side of the switch back to the alternator and + battery terminal in the fuse box would that kill it?

At least everything else is ready. :p

[Matt93SE]

simon, that sounds what I've done with mine. you also want to run a wire from the switched side to your starter if that's not part of the fuse box wiring. IIRC mine went straight to the battery (originally about 3' away from the starter), so when I installed my switch, I ran a dedicated wire there too.
Works every time. :)

[Z3_GoCar]

Both my battery wires go through my BCS, with the small wire also going through a toggle switch to the factory imobillizer relay (avaliable at radio/alarm shops). The relay provides power to the energizer side

[Davegt74]

To revisit this again, I was helping someone over on Honda Tech and went out and checked my ITA CRX

With the cutoff switch to the off position I still have power at the starter and the alternator

This has obviously passed tech many times and I checked the GCR and it passes according to the wording

But does this sound right?


The car shuts off while its running (since it kills power to the ing) but still two components and there wiring still have power

Thanks in advance

davegt74

[Greg Amy]

But does this sound right?
Nope.

The whole point of a kill switch is to remove electrical energy from the entire car, so that nothing is running *and* nothing can spark/short to start a fire. If you have power to anything, then something's wrong.

Without a wiring diagram of your car, there's no way for anyone to troubleshoot what's wrong, but in short you should have a single big wire from the battery positive terminal to the kill switch, then from there to everything else.

I'm going to guess that you have two wires at the battery positive terminal, going to the starter and alternator. Or someone installed your kill switch in some really odd place (like only in the ignition wire).

GA


P.S. Not required by the regs, but you really should have a big fusible link at the battery going to the kill switch. That way if something crushes the wire between the battery and kills switch and shorts it, you're still protected.

[Davegt74]

ok that's what I thought


thanks


David

[Matt93SE]

P.S. Not required by the regs, but you really should have a big fusible link at the battery going to the kill switch. That way if something crushes the wire between the battery and kills switch and shorts it, you're still protected.

Good point. That's always been a concern of mine with the routing of any relocated battery. My cables run along the right side of the car, strapped to the INSIDE of the cage tubing in the hopes that they don't get crushed in a wreck, but I've always been afraid of that happening. I also just ripped the bigass stereo out of one of my old cars and have a fuseholder capable of holding a 400A fuse.. Any idea what amperage I should use?

[Greg Amy]

Any idea what amperage I should use?
Depends on your wire size...most cars are around 12AWG, I'm guessing? that would be a 20A fusible link. Of course, if the power wire is shorted to ground, a battery can probably put out 500A before exploding...I suggest it would be best to size the fuse for the wire you're using.

http://diyaudioprojects.com/Technical/American-Wire-Gauge/
http://www.bdfuses.com/fusesnwires.php

[Matt93SE]

Depends on your wire size...most cars are around 12AWG, I'm guessing? that would be a 20A fusible link. Of course, if the power wire is shorted to ground, a battery can probably put out 500A before exploding...I suggest it would be best to size the fuse for the wire you're using.

http://diyaudioprojects.com/Technical/American-Wire-Gauge/
http://www.bdfuses.com/fusesnwires.php

There's only about a 10 or 12AWG wire going to the ignition stuff, but from the battery to the kill switch/starter, it's a 4awg wire. big stuff. That's the one that concerns me since it'll easily suck up all of the current the battery can put out until it explodes. (don't ask how I know....)