I have an 87 GTA. It has the original 5.7 in it. I put a new battery and alternator in it. The volt gauge doesn't even get up to 13 and when I use the turn signals they blink real slow and the gauge drops even lower. Even when I rev it up it doesn't reach 13 on the gauge. I was planning on replacing the wires to the alternator to the battery and the pig tail for the volt meter in the car. But wanted to see if anyone else has had the same problem and see what they did to fix it.

 

Dude I have the same problem, I also have an 87 GTA and my volt gauge won't pass 13 volts. It's charging at 12 volts. The previous owner on my car did a bunch of Mickey Mouse work on it. For example my fan was powered when the switch was on. I fixed all that bit I've always had this charging problem. My alternator has 4 wires on it but one is cut. I've been looking to see if that wire goes anywhere but I can't find where it was cut from. I removed my instrument cluster and it looks fine. All the bulbs work. I replaced my fuse box because that also had some cut wires on it. Now im just trying to get the alternator harness. Anyways in your case, Have you checked your c/h fuse?