I just picked up a 2000 2DR 4x4 Blazer off a friend for cheap. When I hit the brakes the brakes lights come on just fine but when I turn the headlights on only the headlights come on and the tail lights doesn't. What would cause this problem?

Thanks for the advise in advance.

 

Switch malfunction, break or short in the wire, relay malfunction.. it's possible that it could be the bulbs, but I'm a bit skeptical about all four of them going out like that. The brown wire, IIRC, is the one which supplies power to your marker lamps. Test that with a test light or DMM to see if it's getting power to it. If there isn't, start tracing the wires to find a break or short in the brown wire.