1962 C30 - electric issues?

[Jeepers Creepers]

Hello everyone,
I bought this 62 c30 on craigslist for $1400 not too long ago. It runs well, burns some oil but not tons of it, and has a good tranny. The fenders are rusted out and so are the floorboards, the wooden bed is a loss, and in hindsight I probably paid too much, but I gotta roll with it now right? I'm OK at mechanical things but I really don't know much about electronics. The guy who owned it before me switched out the generator for an alternator, and everything worked fine for about a week after I bought it. But now, if you use the turn signal, there's no telling which light will come on (one, both, or none) and the voltage guage is going crazy. It used to register 12-14 volts, but now it stays on 8 unless you hit the brakes (moves a little) or use the turn signal (sometimes it jumps wildly if you use the signal). Anybody got any ideas? Where should I start? Inside the column at the turn signal or at the rear lights?