Got a mystery on my hands I'm trying to sort out and wanted to get everyone's input. I'm having a problem with my charging system. Here's what's happening.

When driving the car with no heavy loads on, the charging system works fine. The volt gauge reads a little lower than what I think it should but the car starts, drives and charges the battery without any issues. If, however you were to turn a heavy load on such as the rear defroster or the blower motor the alternator outputs enough juice to keep the engine running but can't charge the battery. The rear defroster isn't an issue because no one is going to drive around with it on for longer than five minutes, but twice now I've had the blower motor on high while I was driving around and the next time I went to start the car the battery was too weak to crank the engine.

Now, here is where it begins to get complicated and the sorcery comes in. The problem started right after I installed a set of BBK underdrive pullies. Before we go blaming those however, I DID install the overdrive pulley on the alternator and beside that is the fact that even with the stock size pulley the alternator should be putting out adequate power when the car is moving and the engine is turning at least 1500rpm. At first I tried the pulley set with the stock size alternator pulley and I felt the voltage was too low with loads on especially at idle. I then swapped the overdrive pulley onto the alternator expecting a night and day difference according to member reviews but it made very little if any difference.

I removed the alternator from the car and spun it up on the test bench at work Ans according to that halfass machine the alternator is fine however my multimeter tells a different story. At idle with no loads the output reads high 12s and hits mid 13s at 3000rpm, well over what should be required to get the alternator to charge. With JUST the blower motor going voltage drops to high 11s at idle and barely goes above 13v at 3000rpm.

Now here is the one "clue" to what I believe happened. When I was installing the pulley set which was when the problem began, I accidentally shorted the + post on the back of the alternator. In the past I have blown a diode in the rectifer bridge by doing this and the alternator was only able to keep the engine running but couldn't charge the battery without any loads. I changed the rectifier bridge and this corrected the problem. the rectifier bridge looks fine but something definitely isn't right.

I just wanted to get some input on what the problem could be. Should I start out with the rectifier, the diode trio or could I have possibly damaged the voltage regulator?

 

Probably not the regulator.

When you checked the bridge and the trio with your multimeter, what did the diodes look like?

 

I didn't check them with the multimeter, I simply peered at them through the casing when I bench tested it. The last time I blew one it was visually blown apart. All 6 of the diodes on the rectifier look fine to the naked eye this time.

I went outside and did some more testing and may have discovered at least part of the problem. I'm losing over half a volt through the puny little 10 gauge wire that goes from the back of the alternator to the battery, At 1500RPM the positive at the battery measure around 13.4 while the the post at the alternator measures 14.1v. The small wire is also getting pretty warm to the touch which has fire hazard written all over it. I'm going to be fabbing up a 2 gauge cable tomorrow to go from the battery to the alternator and start with that.

 

I actually just recently had this exact problem. Shorted the + on the back, killed the alt. Did all sorts of weird ****. Just replace it.

Also you're on the right track with hooking the alt to the batt, that's how my Nova is and i'll modify any future vehicle I own to run like that. I used 4 10 gauge wires soldered together.

 

These cars are so weird the way the positive cable splits off into like 4 different places. One to the starter, another to the alt, then 2 more leads that go to the ECM AND the fan relay. Very disorganized cable setup IMO. I'm going to try to find a stock battery distribution block from a 93 - 97 car at the yard tomorrow and redo the wiring system. The engine ground strap and main ground cable I've already custom fabbed out of 2ga copper amp wire and I just finished making the one to run from the battery to the alt. Only the starter is left although I might use a 0ga cable for that. The wires that power the ECM and fan relay I'm going to snip from the battery cable, put some ends on and route them to the distribution block.

 

I believe the problem has been corrected. I installed the fabbed cable and took the car for a test drive. The voltage still appears a Tad low at idle but with the pulley system that is to be expected. At cruise, the voltage now reads significantly higher at the 13 mark (Stock gauge so add at least half a volt to that number) with the high beams on and the blower motor on blast.

The puny little cable (More like a wire) that I removed looked significantly damaged. The electrical tape (The GOOD 3M kind) had dried, cracked and blistered from the heat and the wire strands were blackened at the ring terminal. Like I said before major fire hazard.

Excuse the messy engine bay. I have yet to replace the coolant tank, haven't done a thorough cleanup from the bodyshop and am in the middle of bedlining everything.