So on this Subaru I have ('85 GL Wagon) there are issues with the voltage.

 

When I first drove the car around, the voltage seemed a steady 13.8 or so, but seemed a tad high. There were no electrical issues so I didn't worry about it.

 

This morning, I start the car and at idle, it's putting out about 15 volts. At about 2,000 RPM it would peg to 18volts, and it'd stay at 18.

 

The only issue this caused was the stereo refusing to power up. I drove it to work and home just fine, but obviously I can't leave it like this.

 

I spoke with the previous owner, and he said the car had the same problem earlier, and he replaced the Alternator. That helped, he claims, but now the problem is back.

 

Do you guys think I just happened upon 2 bad alternators in a row, or is something else causing the problem?

Could just be 2 bad alternators in a row. I used to work for Advance Auto, and those things failed on a pretty regular basis.

 

That exact problem happened to my alternator, turned out the diodes were bad. So it was still charging, but it was way out of control.

 

Bench test it at a shop and that's what I bet you'll find.

I had the same problem and it was the wire coming from the positive battery terminal to the little box on the firewall wire the wire fuses.

Your alt has a built in voltage regulator. Pegging at 18 volts on the guage is a normal sign of a dying soob alternator.. if not repaired/replaced, it can fry your battery, which in turn can fry your new alternator.. vicious cycle....

If it ends up frying your battery and you don't know it, you could be in danger cause the battery will explode and acid will go everywhere (like on you if you happen to be working on it and it explodes). Have your alternator bench tested like at Auto Zone, Knects or some place that does it for free. If its not your alternator, well then you could have a wire problem. If the positve cable going to the battery gets corroded and restricts the amount of amperage and voltage, then the alternator will overcharge cause it thinks the battery needs more juice when it doesn't.