I have an 84 gsl se and recently i blew a coolant line causing pretty much all of my electronics to go bad, i replace spark plug wires, battery cable and my alternator. This seemed to fix just about everything, and the car drove fine from des moines to chicago. However the next day the when i started the car the voltmeter read more than 16 volts when the engine was above 2000 rpm and about 12 volts when at idle it was a fairly noticeable difference the headlights along with the interior light would dim when it was at idle and when it was above 2000rpm the stereo stopped working. I was wondering if i got a bum alternator(im taking it to be tested tomorrow) of what else could be wrong?

 

Hmm... Well, I'd say other than a bad alternator, check your battery. A Battery's internal temperature should never exceed 120 Degrees Fairenhiet; it will cause damage to the battery itself.

Also check for any serious power drains that may have resulted from the coolant leak. But I would bet a guess that if your coolant busted, it got on the battery. Or at the very least brought the temperature of the engine bay high enough to cause damage to your battery...

Then again it could just be something else...

 

Bad ground? Bad rebuilds?

 

Check for a bad ground on the starter. That can cause all sorts of problems. Happened to me twice, ended up replacing the batteries, alternators and stuff before I found the loose ground.

 

If it's overcharging at higher RPMS I would suspect the voltage regulator. Your alt should be internally regulated. It's easy to slip off. I would take it off and have someone bench test it for you.

 

Now that you mentioned that, it makes a lot of sense...
Definetly check the regulator, that might be the problem...

 

As stated above, check your grounds.

A bad ground makes the electrical system do some strange stuff as well as kill the regulator in the alternator.

-billy