Alternator charge switch on 1991 Honda civic SI

[somedude88]

I'm looking to get a bit more mileage out of my Honda, I was installing an alternator switch to only function when the brake is applied however... I didn't notice until I doubled checked the schematic and didn't realize there is two Alternator wires on pin B5 being a white and yellow wire and b14 being a blue wire, I have a pm6 ecu. Can't find any description of them. I was using a relay that is excited through a toggle switch switching between normal operation and on only when brake is pressed.

I looked at the schematic involving the alternator but couldn't figure out what to use, my alternator has an internal regulator.

Please help me I was hoping this would be easy, I have one wire left to connect and I'm starting to wonder if I'm able to do this with few parts. I was looking to only get gains in city driving, would use alternator normally on freeway.

FIRST post but long time lurker and been checking out aerodynamics. Installed some campaign signs to the bottom of my car to replace the missing oem engine covers.

Thanks in advance for any help, Derek

[some_other_dave]

I don't know what wire is what, but Google should help you to find a PDF of the Helm manual for your car. (I know there's one out there for the CRX, which is just about identical mechanically to your car.)

Your car, BTW, already has an alternator disable built into it. The ECU reads a bunch of parameters like temperature and current electrical load, and turns off the field current to the alternator when it doesn't think the battery needs charging. It freaked me out when I saw that behavior the first time on the cheapie voltmeter that plugs into the cigarette lighter.

I used to drive my CRX with the fan on to force it to charge because I did a lot of engine-off coasting in it, including some with the lights on.

-soD

[drmiller100]

you need two wires to make a 90 and newer honda alternator work. The big white wire do not mess with - it is the "direct to battery" wire.

IN the harness.there is a black and yellow wire. energize it and the alternator works. remove power and Ground it "gently" through a light bulb, and it will quit charging.

[somedude88]

I have had a digital voltmeter in my dash for a while and I thought the same thing, howere I try to run as little accessories as possible, however I want to charge the battery at the right times if possible.

The wire you tell me to ground, when i cut it is the end coming from the alternator I need to ground correct. Also why do I have to ground it, I was hoping to use a relay to accomplish this with little parts and as uncomplicated as possible. I suppose when there is no power to the relay i could have the connector connect with ground and when relay is energized it could switch to normal

[drmiller100]

the black yellow wire is the one we are talking about.

do NOT just ground it, ever.

if you unhook it, then start the car, the alternator will not charge.
If you then hook it up, the alternator will start charging.

If you then unhook it, with the car still running, the alternator will still charge.

You need to "ground it gently through a lightbulb" to kill the field so it quits charging.

[somedude88]

Will a 5w wedge marker light bulb work? ok so it's on the alternator side.

[drmiller100]

yup.

[somedude88]

I just tried tracing the wire up to the driverside harness connector (on top of shock tower) and I can't find any terminal that has continuity with the connector wire or black with yellow stripe. There are a couple black and yellow wires. I tried them all, a couple show conductivity though :/ Which seems odd

The alternator wire is out of soldering reach under my intake, I can see it though and unplug it to check continuity by putting a multimeter into the proper terminal.

[drmiller100]

if you really dig into your harness, you will find about 50 wires throughout the car, including the engine compartment, which are black and yellow.

There are 3 of them into the ECU alone. black and yellow mean "ignition switched 12 volts" in the wiring harness.


You really need to strip the wires by the connector at the alternator to get the right one.

[somedude88]

Oh ok, well I'll just have to do a bit of stretching I'll just get a couple wires in there and solder to each side to bring it upwards for better access. How much current runs through this wire, seems there aren't really big wires I was maybe hoping to route this into the interior of the car, I don't want relays hanging around the wet engine bay, especially if I have to rely on it for being able to reliably use my car.

I didn't realize that was just an ACC Wire.

Do you think I would have to worry about voltage drop wiring it back to the console to a relay.