Drove home the few miles from work and noticed the voltmeter for my '91 4x4 was on the low side of the guage. A trip into town had the guage even lower so I thought I must be running off the battery. Sure enough, I was only 12.3 volts at the terminals at idle. I checked wiring and found a bad fusible link from the alternator. I replaced the link and still didn't have a change at the battery. Pulled the alternator, split it open and found one lead from the windings free from it's terninal. It looked as if it had got warm enough to melt the solder. I resoldered it and put everything together . I had an improvement in voltage but it was only to 13.5 volts. Everything still looked good after idling for 20 minutes so I took a test run. About 5 minutes into the run the smoke had started to come into the cab. Fortunately I didn't tighten up the battery terminals too tight so when I pulled over I was able to twist the leads off before I lost the truck. Suggestions? Maybe the problem started with an internal alternator short? I'm scared to drop a new alternator in and have it fry in 5 minutes. Anyone familiar enough with a '91 to make a suggestion?

 

I would say that you have a wire possibly rubbed raw, and it's shorting you alternator out completely, which is why the fusible was blown. Did you find out what released the smoke? I would replace the alternator, and the wiring harnesses. I've had some problems with my 91's alternator, but there's not much to them.

 

I would suspect one of the positive wires has been rubbed raw against the frame and giving you a direct short. I would start by tracing all the positive wires to the fuse box. Since you are not blowing fuses, it must be before this protection. There's a possibilty that the voltage regulator is bad also.

My local alternator shop offers to test things for free if you bring them in. I would suspect that you have (or had) a good alternator since it was producing current for you, but we really don't know. A good alternator shop will help you with the process of elimination.

Greg

 

Any autoparts store should be able to test your alternator for you...

 

I just picked up an alternator at the autowreckers (3 month warranty, both plugs for $75 Cdn). He gave me back the old alternator and it looks like it first fried the plastic insulator around the soldered terminals (nothing left) and the windings have obviously gotten very hot and crispy. I still can't tell if this was an internal short so I'll replace the damaged wires and fusible links and then try out the volt meter to see if I can find a drain in the circuit. Any other suggestions? At least this is a vehicle with a lot of room to do repairs. I wonder if anything will show up on my code reader?