Electrical issues on an '87 Z31 NA

[AndrewKFM]

So, I've got an 1987 Z31 NA that runs (or did until now), and an 1986 Z31 NA, that crashed and doesn't run, for parts and whatnot.

I went to start the '87 the other day, and it didn't have quite enough juice. Lights would come on, windows and radio worked, etc, but couldn't get enough volts to start the car. It would turn the engine, but not enough.

My battery is only a few months old, and I hope it's not the problem.

I jump started the car, hoped in, turned the light on, and it started to die. I quickly turned them back off, and it jump back to life. I tried the windows, and it started to die. I stopped, and sat there, assuming the problem was my alternator, then the car just died on its own.

One would think alternator, yes?

So, the next day I decide I'll pull the alt from the '86 and put it on the '87, and, just for giggles, I went to try and start the '87. This time I got absolutely nothing. No lights, no tick, nothing.

Do bad alternator commonly draw from the battery? Do I just have a dead short? Do I have a bad alternator and a dead short? What should I be looking to do right now. I don't want to swap the alts unless it's likely the problem, so some guidance would be much appreciated!

Thanks,
Andrew

[Perrenial Badass]

What did the gauge say the alt was charging at? All else fails you could have an Autozone/Advance check it, but that would involve getting the car to them so...

Check the terminals to make sure they are tight and free of corrosion, and throw it on a charger. Car will run for a while just off of the battery, at least long enough to read the gauge.

[AndrewKFM]

So put a charge on the battery until a multimeter was reading about 12 volts. Turned the key to "On" and the car's gauge read just a hair under 12 volts. Started the car successfully, then put the multimeter on the battery. Revving did not effect the readout, and the volts actually dropped a little as the car idled.

I interpret this to be the alternator, so I'll be swapping the one from the '86 unless I fail at understanding what this means.

Thanks!

[LunarShroud]

sounds like the alternator to me. typically, alternators charge around 14 volts, don't they? I would also check the wiring and terminals, like PB said.

[AndrewKFM]

Just an update. Got the alternator out of the '86, and got underneath the '87. Turns out the alternator was not only loose, but the belt was absolutely destroyed. It serious looked like a joke. I'm pretty sure the belt was not even engaging the it. Gonna throw a new belt on, tighten it up, and hope the alternator itself was fine.

[AZ-ZBum]

Oh great. No belt on the alternator? I hope you didn't overheat the car at the same time.

[AndrewKFM]

Well, revelation upon revelation. Last time I drove it, it was too hot. Good thought. Geez, I'm glad this is getting fixed.

And the belt was on, it just wasn't doing much. I'm sure it was grabbing occasionally, because I did see the fan spinning at one point, after the alternator was deemed bad (or thought to be bad).

Aaaand I'm confident that belt squeal will be fixed now too. Lesson learned: When I hear a belt squeal, fix immediately.