This is my first post so please bare with me. I recently traded an s10 for my camaro and since have been through 3 alternators. The car is an auto 3.1. 3 wire alternator. The P.O. melted the fan fuse holder and as I understand the signal wire is supposed to run through the fan relay which has been bypassed by a manual fan switch. So my tries for fixes so far have been first a new battery no change. I ran an 8ga wire from the alt. Post to the + terminal have replaced the battery connectors.When I get a new alternator I immediately test it with the multimeter to rule out a bad reman. Reads around 14.7 after installation. All good. Drive a half hour the volt gauge drops from 13 to about a 10 and bounces back and forth same process down to 8 then finally death. Jump the car pull out the multimeter alternator reading about 10 and dropping with battery. No charge. Killed another alternator. I believe it to be the small brown signal wire but I'm not sure how to check I've read to test the continuity and make sure the signal wire isn't grounding. I just can't figure out what is causing this. Bad ground? Bad signal wire? If so is there a way to bypass the signal wire since the po fried the fuse block where the fan fuse goes. I'm at a complete loss and I need to get this car running. Please help!!

 

Update: I've been tinkering with some continuity tests with the signal wire but I'm having a hard time following it. Leave it to gm to run two brown wires right next to each other at the firewall block. I can't get the car to stop killing these alternators. I checked power from post to terminal on alt. 12v. Smaller red wire out of pigtail. 12v. Small brown with key off. Reading a .5? Thought it should dead? Key on tested brown signal wire agaim 56v??? That has to be a problem. From my reading it should be 12v with key on for signal wire? If that's correct what could cause this massive spike?

 

Although this does sound like a wiring issue, I will mention my past history of killing alternators.. I will also try to make the story short.
Somewhere down the line my car received headers (brother had installed at some cheap shop). When the mechanic was bolting the headers on he/she decided that the rear bracket for the alternator got in the way of the headers and threw it out! When the car got to me I found out the hard way that it likes to chew through alternators due to down force form the belt (without the rear bracket force was physically cracking the alternator). Found the issue, made a custom bracket, pissed off autozone after going through multiple alternators leaving them scratch their heads... So I would check your alternator for physical cracks or if you've had mods in the engine bay check for missing hardware / brackets. Yes, my situation was just stupidity, but stuff happens.