We swapped the 86 alt for an 88 style when doing the 3800 conversion. The factory aux gauges were removed and replaced with AutoMeter units. When the car is started the alternator won't charge and the voltage stays around 11.

We left the existing wiring harnes to the aux gauges so we simply plugged the aux gauges back in and the alternator will turn on and charge immediately. The alternator is brand new.

I'm guessing this has something to do with the charge circuite and lightbulb/diode activity?? Is there a way we can simply splice a diode into the system so that the autometer gauges can be used with the factory aux gauges removed?? Also what diode would be needed to do this?

Measure the resistance of the bulb used for the idiot light, scoot over to Radio Shack and pick up at 10-cent resistor to match, wire it in as if it's the OEM idiot light.

quote Originally posted by dguy: Measure the resistance of the bulb used for the idiot light, scoot over to Radio Shack and pick up at 10-cent resistor to match, wire it in as if it's the OEM idiot light.

That may not be the best idea, but would probably work. The resistance of a light bulb is not the same when its off compared to being on.

Can the alt be wired like the original 3800 alt was wired?

[This message has been edited by Ken_86gt (edited 05-29-2006).]

It probably could be wired that way, but the harness is set up for the fiero alt. The charging system works great when the aux guages are plugged in, but unplug them and it won't turn on. One of the guages replaced was the oil pressure, so this has to get sorted out before the car can be driven otherwise that copper line that feeds the mechanical gauge could risk cracking. 80psi of oil through that tiny line would not be a good thing..

wire a light bulb into the circuit

There normally isn't a charge indicator lamp installed in the rally gage. There is another one in the instrument panel wired in parallel with the socket in the rally gage. Only one or the other should be installed and it's usually the one in the main instrument panel. If you use a resistor, 510 Ohms, 1/4 Watt is the correct value. The diode (if present) is in the harness so no need to add one.

I had similar problems with my Allante alternator charging. I went through two alternators and two guage clusters and couldn't get it to charge. I finally had a local Alternator rebuilding shop build me a single wire self regulating alternator. It has one wire from the B+ terminal to the battery and it regulates on it's own. You might check into getting one if nothing else works.

Otherwise, I talked to Darth Fiero about this when I was troubleshooting my problem and he said on the 3800's he usually hooks up the brown wire (L) to the lamp in the dash and the (S) wire to the battery. The B+ is also hooked up to the battery. It should charge like that. Good luck.

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-Rick Stewart
85GT 5.0CaddyV8/Getrag 5-spd
234HP and 304lb/ft at the wheels
www.V8Fiero.com

We'll try the resistor and see what happens, next thing is to find the wiring to see where to splice it into the aux gauge connector harness...

Can't remember the resistor value but the 84's used a resistor instead of a light due to them having a volt meter. Dan

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Signature compliments of F-I-E-R-O
2003 3800SC series II powered
www.photosled.com/showgallery.php/cat/631

We put a resistor (470 Ohm 1/4 watt) into the stock AUX guage pins 1&2. It works flawlessly. Even tried running the car without it and the alt didn't charge, the instant it touched the 2 pins, right up to 14 volts.

Thanks.

[This message has been edited by Jncomutt (edited 05-31-2006).]