Intermittent issues with my charge lights

My charge and sensor lights will not go off now, battery not being charged.

I first re-soldered the charge lamp relay and this fixed it for a few drives. I then checked and cleaned all grounds, replaced the IR regulator, new battery, new alternator, installed a new brake sensor... Basically everything I've found reading through forums of fixes for this.

When I would get a charge, it was right around 1500rpm before the light kicked off and the battery would charge. I made a handful of trips and I'm back to under 10v on the dash meter with charge/sensor lights on full time.

I'm not mechanical or electrical at all, and I'm really just lost on what I can do at this point to fix it myself. What's getting me is that it was working fine randomly. HALP!

 

So I took it out tonight and the charge/sensor lights will only go off above 3500rpm, which scares me in this old thing. It starts visibly charging and goes above 12v when I maintain the 3500, but quickly drops back down to 9-10v once the light comes on.

 

Took the alternator in today and it checked out okay. Shop said it was the voltage regulator that wasn't working properly. I took it off and looked at the pigtail, and it looks like one of the wires is fried. Now to find the pigtail for that... I've searched all over and no luck thus far.