2000 Civic Si Master Switch

[backformore]

Hi all. I know there are tons of posts about master switch wiring and I've looked at most of them. I understand the general goal, but hope someone can answer a specific question.

I have a Longacre double-pole switch with a large normally closed contact and a small normally closed contact. As I understand it, the proper way to wire this is with the large contact for the Battery cable and the smaller for the alternator field current. By breaking the field current the alternator should stop producing power immediately and prevent damage to the alternator.

My question is, based on the attached diagram, which wire should I run through the switch to kill the field current when the switch is opened?

It seems to me that it is the BLK/YLW wire from Main Power Distribution to the ALT.

Thanks

RORY

PS Please chime in if you feel I need the 6-pole switch with the resistor in order to protect me alternatorrsz_civic_si_alternator_wiring.jpg

[Greg Amy]

Anything that will stop the car dead is fine; on the Integra I cut the main ECM power wire. I *suspect* - but don't know your car and would want a full wiring diagram to be sure - that if you cut the WHT/RED wire going to the ECM that might do it.

But don't cut the red wire. Never, ever cut the red wire. Always black.

[backformore]

Thanks for the quick reply Greg. Since you have lots of Honda experience, is there any method that risks damaging the ALT more than others?

Also, do you mean The black (GRND) vs. Red(POS) on the battery too?

[Greg Amy]

Thanks for the quick reply Greg. Since you have lots of Honda experience, is there any method that risks damaging the ALT more than others?

Not necessarily. You'll use the included resistor to "slowly" drain voltage to ground instead of arcing the internal contacts of the switch. Otherwise it's the same as turning on your ignition.

Also, do you mean The black (GRND) vs. Red(POS) on the battery too?

No, I'm referring to every bad 1970s/80s cop show that included a bomb disposal team.

Always cut the black wire.

[autoxmike]

I've gotten away from using a cut off switch that has the smaller secondary contacts. I've had 2 of the secondary contacts go bad and I know of several other people that have had similar failures. Now I use just the primary, heavy duty, circuit to discontent the battery. To make this work I connect the alternator output directly to the battery on the battery side of the switch.

[backformore]

Great! My first thought was that you were referencing said shows, but I just wanted to be sure!

As for the other, the switch I have does not have normally opened contact or included resistor. Just 2 contacts, a large and a small, that open when the switch is selected off. I was hoping that killing the field current, it would cause the ALT to "turn off" thus preventing damage without needing to "drain" any voltage.

If that is not the case, I will just have to get one of the OMP switches with 3 contacts.

[Greg Amy]

That switch sounds like it will work fine.

The one I'm using has a second circuit that's open when the switch is on. One side goes to ground through a resistor, the other side goes to the chassis terminal of the big red wire (NOT the battery side). Its purpose is to allow any remaining voltage in the chassis to "slowly" bleed to ground when the switch is opened so that the big terminal contacts do not arc. If yours doesn't have that, don't worry about it.

Cutting the field circuit is not for "safety", it's so that the car will stop. Most alternators will continue to product amperage with the battery disconnected, thus the car won't stop running when you disconnect the battery. Cutting the field circuit so voltage goes to zero and/or cutting some ECU power feed wire will ensure the engines stops running when the master turned is turned off.