Battery wasn't charging (so car died in middle of road once juice ran out), but tested fine at auto store I took it to.
I don't have enough knowledge to really test the alternator properly, so I took a chance and decided to replace the voltage regulator. Did it today, seems to have solved the problem. When I turn on the car, dashboard lights light normally. Battery shows 13.xx volts with car on. The old voltage regulator's brushes were worn - the one closest to the outside (closest to the casing) was REALLY worn down. So, I'm optimistic that it's all fixed now.

The thing is, I had a really hard time getting the new regulator in. I couldn't figure out how to keep the spring-loaded brushes down while I inserted the regulator. Without them down, they block the way and the regulator cannot be inserted all the way. After lots of fiddling, it somehow got in. But it took a long time, and it was just luck, and I was beginning to think I was going to damage the regulator but trying so much. For the future, and for others' reference, does anyone know the best way to do this?

Thanks