I've been having trouble with the charging system for the past week. At least, I think. The battery went dead exactly 1 week ago after a long drive (6 hours with a break in-between). The car sat for 2 days after the trip, and then barely had a click when the key turned. Replaced the battery, and the car ran a few days before dying on the road not far from home. As it was dying, it drove very slow and sputtered, lights dim, and instrument panel dancing weird. The lights were on, and when I would turn them off, there was an instant power surge, and occasionally I could put the lights back on and it had enough power. The voltage going into the battery (haven't directly checked the alternator voltage yet) was 13.0 volts before then. Replaced the alternator brushes, voltage went to 13.5 (at 2000rpm) for a while, then after running the car for about 20 minutes and experimenting with different loads and idle speeds, the voltage went to 12.8. Something may have disconnected, I will check tonight.

The question is, am I headed in the right direction? What else should I check for? I just read about testing voltage drop, but I'm still not exactly sure how that is done. I understand for the negative battery cable, but how does one test the positive cable? I have only a cheapy 10A multimeter... will I ruin it by testing voltage drop?
I also read in the faq of a wire coming out of the back of the voltage regulator. On my 740 I only see a wire coming out of the back of the alternator opposite the red/black wires (but nothing from the regulator). When I first saw this wire, it was hanging loose, and it looked like it had been attached to the engine block, so I re-attached it. What is the proper order of connections here?

I'm open to any advice, as I'm a starting DIYer, and a starving student at that. Many many thanks!