I am having some difficulties getting my alternator to charge my battery. I have done some testing and was hoping someone may have some insight into my problem. I have a brand new alternator, that didn't help. I read that if there is a problem with my fan switch the alternator would not charge, I have rewired it and gotten it working. Here are the results of my wiring checks.

If I turn the ingnition to the on position and check the voltage on the large red wire that goes to the alternator post I get no voltage. If I put 12v on that post it engages my starter solenoid. My car runs so the side of that going to the starter must be fine.

I have 12v on both of the wires in the pack on the alternator.

If I take 12v and apply it to the main post on the alternator I hear a faint whine in the alternator. Does this mean the regulator is being activated? This was done with the large red wire unattached.

If I were to get a one-wire alternator would it work on my system? I have a 92 305 TBI Firebird. If I were to take and wire a bypass 4 ga wire to the positive battery terminal directly to the alternator would that work? Would that provide a test to see if my charging system is working properly?

What should I get as far as power on that large red wire when the ignition is on? Should I be getting 12v? If anyone knows how I should go about correcting this, your input would be greatly appreciated.

 

the post on the back of the alternator should have power any time the battery is hooked up. that post is the output.

the other red wire should also have power at all times.

it sounds like you have something wired wrong. according to my wiring diagram, the wire from the post on the back of the alternator goes to a junction block & has a fuse link in it near the junction block, from there it goes to the battery positive terminal.
the other red wire goes to the battery terminal on the starter & also has a fuse link near the starter. i think this may be where your problem is, the starter should not engage with any of the alternator wires being powered up, make sure you don't have the wires crossed at the starter.

 

My wiring is all screwed up as well. 91 305 TBI . The junction block you mentioned is there but all the wires are in a ball of tape??? It was in that mess I found the fuse to the fuel pump and replaced. ( car lot thought fuel pump was bad, got the car 500 cash, looks and runs great.) The alternator has that faint hum constantly that was mentioned. I checked with the local parts stores and the alternator is the correct one for the car. With that being said I can't for the life of me figure out why they have spliced into the harness going to the alternator. The wire from the back they have running to the terminal on the battery. The other red one from the plug runs to the tape ball of wires (junction block). The other, I'm assuming is a ground, I can't find where it runs. The hum keeps draining my battery if not ran every other day. I am getting frustrated with this. Not to mention their ingenius ball of tape is eventually going to burn through and start arcing off the radiator support and that probably could be something fatal for the electronics of the car. If you guys can make any sense of this and have any help it would be greatly appreciated.

 

BlueSmoke, you can run the 2 red wires off the alternator right to battery positive. thats where they go anyway, they just take different paths.
on my car i have the red wire coming off the plug on side of the alternator ran to the post on the back of the alternator & then it goes to the battery through a fuse link. the third wire on the alternator comes from a switched hot with key on source. it should not have power when the key is off.
with the third wire powered down or disconnected, your alternator should not make any sounds with the motor off, if it does your alternator is bad.

 

Thanks alot for the input on this. I had completely forgot to check this thread again. It was this morning when I went to start my car and it was drained I rememered about this post.

OK the 2 red ones to the battery and the 3rd should be hooked up to a hot key on source. If I disconnect the 3rd I should hear nothing, if it's not silent alternator is faulty.


Where would the hot key on source tie in from the factory?

 

Alright I opened up their splice. They had the brown hot key wired into the red one off the plug, I'm assuming because the brown one has no power at all at any time. Quick fix I ran a jumper wire to the fuse block. The problem is, could be the way it's wired, is volt gauge. It should be around 14 with a healthy charging system right, it's bouncing from 13 to around 10. Goes up a little more when you give it gas and almost bottoms out when sub/headlights/heater is all on. The alternator on my 2.8 is brand new. Advance say they are both 105 amps and same wiring but they mount completely opposite of each other. I don't have my 87 in front of me to look at the difference. Is this switch possible or not? Again where does the brown wire get it's key on power from.