Kill switch dies

[c2ron]

We are scratching our heads by an odd problem with an ignition kill switch in a Spec RX7.

The old four post switch was causing a battery drain. We'd get 14 volts at the alternator, 9 at the battery. So, we replaced it with a Sparco 6 pole switch. We didn't use the two auxiliary posts.

Initially, this seemed to work. 14 volts at the alternator, 13.3 at the battery. At idle, flip the switch and the engine shuts off.

However, if we rev the engine up, flipping the switch does nothing. When we let it go back to idle, it will again kill the engine.

Anybody have any ideas?

[dickita15]

The alternator is supplying power to keep the engine running. The switch is wired wrong. As was the old one I suspect. On my car the large wire from the positive post of the to the starter is rerouted thru the 2 large terminals on the kill switch. The number 10 wire out of the alternator goes to the small terminal on the switch and then from the switch back into the harness where the alternator output went previously. This isolates both the battery and the alternator from the car when the switch us off.

[AntonioGG]

If you wire it like Dick recommended, you also need to use the 3rd pole (set of contacts) which is probably a normally-off (i.e. when the other poles are on, this one will be off), to hook a power resistor to ground so when you disconnect the alternator and kill the battery power the energy from the alternator has a place to go until it stops spinning.

[JimLill]

see http://www.scca-nnjr.org/spec-corner/technotes-01.html

[dickita15]

If you wire it like Dick recommended, you also need to use the 3rd pole (set of contacts) which is probably a normally-off (i.e. when the other poles are on, this one will be off), to hook a power resistor to ground so when you disconnect the alternator and kill the battery power the energy from the alternator has a place to go until it stops spinning.
[/b]

I have read before about using a resistor to protect the alternator but at least on the 3 or 4 Rx7s I have wired this way I have never had an alternator problem. I don’t know if some systems are more fragile than others.

[tom91ita]

here is a similar thread:

http://itforum.improvedtouring.com/forums/...=7230&hl=switch

in it, i posted a link to photos of the schematics of how i wired my Honda:

http://pg.photos.yahoo.com/ph/tom91ita/alb...m/ph//my_photos

can't hurt, could help.

tom

[tom_sprecher]

I read where if you use a 2 pole switch that is made for use as an E-switch that when you turn the switch off the smaller pole is disconnected fractions of a second before the main pole. This allows the field to be disconnected from the alternator before the battery is disconnected fro the rest of the car. Any current flow left from the alternator goes to the battery and the output drops to practically nothing due to the absence of the field. That's how I wired my IT7. Do a search on this subject as many threads have been posted.

[AntonioGG]

You can do it with a single pole switch.
I'll post a diagram later tonight.

[c2ron]

Thanks, guys...lots of good info.

The problem with searching on this topic is that there are so many names for this widget..kill switch, battery switch....never searched under master switch.

The instructions supplied with the unit are fairly useless, but the drawings some of ya'all posted help a lot.

[tom_sprecher]

I tried to post a wiring diagram but it cut out a lot of the lines when it uploaded. Email me and I'll send it to you.

[callard]

On older German cars, does anyone know which alternator wire (B+, DF, D-, D+/61) should be connected to the resistor so that when the master switch is turned off the resistor is attached to the wire?
Thanks,
Chuck Allard

[AntonioGG]

Dave Wheeler posted this method on the SM website.

It will work for a SRX7 as well.

Personally I used a bigger wire (6-8 AWG instead of 10-12AWG).

Dave prefers not to have fuses b/c of reliability issues.

I wired mine just like he did but considered adding an 80A fuse on the new wire and not looping the unused wire that went from the starter to the alternator B-terminal (Dave also doesn't like to cut stock harnesses). He's been involved in car racing for a while so his opinion is well respected.

[wrankin]

I'll be the first to admit that my knowledge of auto circuits isn't perfect, but:

1) don't you want a fuse between the B-terminal on the alternator and the + battery post?

2) your circuit has you bypassing the 80A fuse between the starter and the ignition switch, which I don't believe you wanted to do.

-b

[AntonioGG]

B,

Read the text before looking at the picture.