Alternator Charging Q - Power Pulley

Chris-Nelson · Post by **Chris-Nelson** » Tue Sep 11, 2007 12:25 am

I installed a Fiero Store Power Pulley on my '85 with the 3.4L v6 and now my alternator does not charge, it was working fine before I installed the pulley, maybe it's just simply belt tension.... I have 2 alternators on hand and I have had them both recently checked over by a local shop (within a week) and they were working very good.

I pulled the one out that was in the car and installed the other and still no charging.

I cleaned all of the terminals really well and actually put a new connector on the heavy red wire for the battery. I know that the 2-wire plug is sitting well on the correct spot and making good contact.

I tested resistance between the alternator lug and the battery lug and got 0.3 ohms resistance. That cable is good.

The battery light comes on when you turn the ignition on and stays on after the "bulb test" circuit does it's thing.

What could be causing the alt to not charge? What do the two wires on the alternator do? I know that one is connected down a few inches on the battery wire, but what does the smaller brown wire do?

Also, is there a way to do a diode check with a digital multimeter?

Thanks!!

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Club Redline - Northern Minnesota Sport and Modified

Fastback86 · Post by **Fastback86** » Tue Sep 11, 2007 2:51 am

Probably not spinning fast enough to charge properly.

Series8217 · Post by **Series8217** » Tue Sep 11, 2007 3:04 am

The brown wire goes to one terminal of the charge bulb/battery light.

The Dark Side of Will · Tue Sep 11, 2007 7:48 am

Have you tried increasing engine RPM until the voltage comes up?

What's the condition of your battery?

Chris-Nelson · Post by **Chris-Nelson** » Tue Sep 11, 2007 6:59 pm

The Dark Side of Will wrote:Have you tried increasing engine RPM until the voltage comes up?

What's the condition of your battery?

I watched my DVOM with the vehicle running and revved it up to 3K or so and still no change in alternator activity. I'm going to toss the old pulley back on and see what happens then.

Also, the battery is an Optima Red Top that was new in late 2005. It tests to be in very good condition.

coinage · Post by **coinage** » Tue Sep 11, 2007 11:15 pm

i know when my brother put an underdrive pully on his 87GT he was having problems with the charging system... my bet is that it is related to the pully

Chris-Nelson · Post by **Chris-Nelson** » Tue Sep 11, 2007 11:18 pm

I have a hunch that the combination of a pair of old, used alternators together with a smaller crank pulley = charging issues. I'll switch pulleys and if that fixes it I'll just keep it that way until I can upgrade to a better high-amperage late-model style alt.