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Thread: 2000 Civic Si Master Switch

  1. #1
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    Default 2000 Civic Si Master Switch

    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

  2. #2
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    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.
    Not my circus...not my monkeys...

  3. #3
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    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?

  4. #4
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    Quote Originally Posted by backformore View Post
    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.
    Not my circus...not my monkeys...

  5. #5

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    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.
    _____________________
    Mike Taylor
    1995 MX-3 LeChump/ITX

  6. #6
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    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.

  7. #7
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    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.
    Not my circus...not my monkeys...

  8. #8
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    I have the black with yellow wire that powers the ignition coil going through the small terminals on the switch and the large terminals on the switch connected between the negative side of the battery and the chassis ground. On my ITC CRX, normally the only time the switch gets turned off with the engine running is when it is tested in tech. When that happens, I turn on headlights, taillights, brake lights to act as the resistor. I have never had a problem by doing this in the 15 years I have raced this car.
    Will Perry

  9. #9
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    Thanks Will. That is great info. The headlights etc is a great idea. I'd already thought that in a real emergency I don't really care what happens to the ALT so the testing is the only time it matters. Thanks again.

  10. #10
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    on our hondas, including a '99 Si (same as your 2000) we always replaced the stock cable from the battery to the starter and main fuse box with a new cable to a switch mounted inside by the left wing mirror. Return cable to the starter then up to the fuse box in the stock location.

    Cut the IG1 line from the key switch and run it through the smaller NO contacts on the switch. this will kill the car and not create an alternator issue. and it's easy.

  11. #11
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    Thanks chip. I thought it looked like it should be that simple, but I appreciate the first hand info. Really wanted to avoid doing unintended damage. Just to clarify, the contacts the IG1 goes through are closed when the Master Switch is ON , and open when it is off. Correct?

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