Ok, so i tried to do a little research before asking(probably not enough) but here it goes. On my 70 cutlass, my head lights and front marker lights work and brake lights and directional's work but tail lights and rear markers don't. headlight switch?

 

Fuse? Ground?

 

Do your instrument panel lights work?

- Eric

 

You might want to spend a few minutes looking at the wiring diagram for your car. The front and rear park lights are all powered from the same contact on the headlight switch, so if the front running lights are working the switch is good, as is the fuse and power source.

The parking and side marker light circuit is a brown wire from the switch. The wire is spliced right at the switch (the front and back wires are crimped on the same terminal in the connector). The problem is somewhere between that terminal and the rear bumper. This wire runs in the flat bundle under the carpet and into the trunk behind the back seat, then along the underside if the trunk weatherstrip channel to the bumper. You will need to trace this wire to find the problem. There are two connectors in this bundle (the most likely source of the problem), the front body connector near the dash (not to be confused with the firewall connector) and the rear body connector.