Check the key on voltage at the regulator in wire from key on.
sometimes the bulk head connector is bad.
I had that problem last year and it was a poor connection at the regulator thus it was showing low voltage at the regulator so it kept telling the alternator to charge full. Would boil the battery.
sounds like you may have bad connections at the bulkhead to the lights too.
Oh grounds grounds grounds make sure motor is grounded to battery and at least two body places. (I like three grounds off the motor 1 to battery and 2 to body! Battery needs a ground - to body also.
Headlight system has a ground too make sure it is good!
) if you had an ammeter it could help in determining what the voltage is doing. Before I get flamed, I do prefer an ammeter over a voltmeter, but being an electrician I really would prefer both.