I have done searching on the forum for this issue and had little luck with my problem.

Car is an 87 GTA 350 TPI with analog gauges.

As other threads suggested, I have tested for power at the alt with the key off and then on. The plug is 3-wire and most the advice was for a 2-wire.

I have no extra power going to the plug with the key on, only the heavy gauge red wire.

I checked for the light in the cluster that others said should be on when the key is turned but no "battery" light comes on or is present in the cluster (140mph speedo). The choke light also does not come on even with a good bulb and socket as others have again suggested.

If any of the info above does not pertain to my year let me know please.

After testing all the above I am still not getting any power form the ECM to the alt. Are there any specific fuses that could be causing the issue or what should I test next.

 

Those lights are not used on the TA's with analog, we have Gauges,The only lights that come on when you turn the key are "Service Engine" and the Seat Belt lights.IIRC their used on the Firebirds with the Idiot lights.

 

I see that's good to know, I didn't find any info specific to my car but wanted to try the suggestions before starting a new thread.

Where does the signal for the alternator come from on the GTA?

 

bump

 

I guess it comes from the Alternator to the gauge.

 

Does anyone have a wiring diagram or can point me in the right direction for one to track down the signal coming from the ecm to the alt?

 

The signal does not come from the ECM on these cars. The newest systems use signals from the ECM to control voltage and turn the alternator on and off but not any third gens. Most older systems use a light as a load to limit current to the stator of the alternator to "excite " the alternator until it starts producing a voltage at which point it becomes self exciting. There are wiring diagrams at AustinThirdgen.org for your cars charging system which should help. GL!

 

According to the diagrams, you should have 12 volts on 2 wires of the three. The battery to the alternator and another red wire which comes from the battery but through a fusible link. There is no light shown so I guess they just excite the alternator from the battery directly (through the fusible link). HTH!

 

The fan fuse in your fuse panel, check that. There has to be a good fuse there or your alternator won't work. I've been a victim of that one before.

 

On the alt I have power from the main line on the alt stud from the battery and then power on the red wire in the 3-wire connector. I have checked the other wires on the plug with the key in the "on" position and neither of the other brown wires are getting power. I have checked the fan fuse in the box and the fuse is all good.

Thanks for the responses, I appreciate any help

 

Okay, just had a thought but it may be stupid.

My cooling fans are both currently unplugged because they were draining the battery when the primary fan was on and trying to start the car when I started working on it. I haven't had it running very long and haven't plugged them back in, would that cause an issue with the alt circuit?

P.S. Thanks for the AustinThirdgen info wiring diagrams are great

 

I don't think so. I don't have the stock wiring for the fans connected, but still have to have the fuse in. PO didn't one helluva hack job V8 swap, and cleaning up the wiring has been a PITA.

I can't remember, is the 87 the later or the older style alt? I believe the older one has a voltage regulator bolted on the outside of the alt. Been about 13 years since I've had an 87 or older, can't remember for certain. I do remember pretty much having a helluva time figuring out why one wasn't charging, but can't remember if it was my 84 or 87.

 

The alt I have has the stud for the main wire going to the battery and then the 3-wire plug with a red, brown, and brown and white wire.

 

Silly question, have you had the alternator tested yet? I haven't seen that stated. There have been times where I was sure that something couldn't have been the problem because hell, it was only a month or two old, and sure enough, the part that couldn't have been bad was.

 

Yea I had Advance Auto Test it when I took it off the car and it checked out

 

Tension on the belt is good, battery is good? You said the fan fuse on the fuse panel is good too. The only other thing I can think of is a bad wire. Otherwise, I'm at a loss. I've had stuff test good at advance and not be good, but idk, man, wish I could be of more help.

 

Battery and tension are good I believe. Based on the wiring diagrams suggested earlier There must be a bad wire or something because the diagram says the brown wire in the plug should have power when the fans have power from the fuse box but I amnot getting that power to the plug.

 

Try connecting the brown wire to the red wire using a jumper. It won't hurt just to test to see if the alternator starts charging. You are correct according to the diagrams, you should have battery voltage on the brown wire. If the alternator then charges, you know for certain that is the problem and then can trace the brown wire back to see where you are losing the voltage. HTH!

 

Well I found a bad spot where the wires had been replaced and the splice was no good. I ran new wires to the alternator connection and I am getting 12v with the key on now to the brown wire.

With a multimeter I am getting ~12V at the battery when the car is running, is this normal?? I thought I should have around 14 or so if the alt is now working.

Thanks again for any help

 

Should be around 14

 

Well here's a puzzler... still working on the car a bit today and I held the engine at a little bit of a rev and all of a sudden the voltage gauge went up to ~15 on the dash. I checked the battery and alt sides and both read just about 15 for a little while and then slowly dropped back down

The belt seems to be plenty tight on the alternator

Has anyone experienced anything like this before

 

Sounds like it could be the diode trio.There is a small black cover on the back of the alt, remove it & you will see 3 diodes.If one (or more) is blown.You've found your culprit.

Voltage at the batt should be 12v w/ eng off, 13.8-14.2 w/ eng idling & lights on.