86 brake, tail, and turn signal probs.

I have a 1986 Chevy K10 and this just started happening the other day. Both tail lights look like they are out. Bulbs look good though. Brake lights don't come on either when I hit the brake pedal. The flashers work though. Both front and back flash normally. The turn signals, both front and back work when I turn them on. Except for when I turn the headlihghts on, then they don't. Not sure what kind of electrical mess I have here. Has anyone seen anything like this before? Thanks!