charging system woes...
 

this is really weird.

I replaced the voltage regulator today and went out for a drive tonight... the first 20 minutes seemed normal.. dash, headlights, interior lights, all bright. After then, the I can tell the instrument cluster lights dimmed significantly. It happened suddenly, not gradual at all. After about 5 minutes of this, at a stop light, the interior lights went back and fourth a few times between dim and normal (whilst changing the idle speed, but this is understandable because of the lower voltage affecting the ISV), finally back to normal. By this time I was just pulling into my destination and turned it off in a few minutes. It started up fine and acted normal all the way home (about ~30 more minutes).

Same problem as before.

What else could there be? I didn't expect battery, because of how quickly the problem comes on and off, I thought it would probably be gradual if it were the battery, but maybe not? I didn't think it was a ground, because it didn't seem to be affected by going over bumps or anything, maybe it is though. Does the alternator go to a common ground?

Thanks.

how is the ground strap at the battery?

at the battery terminal it's fine
 

I kind of ruled that out, because if there was a poor connection to the battery, then the alternator should produce enough power to power everything normally.

So I concluded that it's an intermittant charging problem.

goto a battery shop and have them test you.
 

they got stuff to see voltages. and its free.