Electrical/headlight issues

[zac]

Had my '79 K20 about 3 years, spent most of that time undoing the abuse of PO's. Always seemed to have electrical issues. With headlights on the oil pressure dropped, temp gauge went from normal to almost pegged, volts down near the the orange arc. Turn the ligthts off and everything goes back to normal instantly. Headlights would "surge" meaning brighter or dimmer depending on RPM, expcept that at idle they were usually normal with volts normal, except when they weren't. Found and fixed some hilbilly wiring at the alternator, swapped on an alternator I believed to be good from my shelf. Same problem.

At cruise speeds the lights will randomly dim, then brighten up. Voltmeter shows volts going up and down. I can goose things back to normal temporarily by popping the throttle. Seems like a regulator problem to me, but hard to believe both alternators have the exact same problem. My next plan was to swap the light switch and dimmer switch, but I doubt that's it. Would look for short in headlight harness, but blower motor seems to cause the same problem. Maybe a ground problem? Any suggestions? Thanks