1972 Chevy c20 inside lights and brake lights and signal lights not working but front lights are why?

Bulb Troubleshooting (check in this order):

· Check Fuses

· Check Bulbs

· Check Relay(s)

· Check Light Switch(es)

· Check license plate light bulb and wiring

· Check trailer hitch wiring harness

· Check all wiring harnesses and wire

Most likely its the fuse or a burnt bulb breaking the circuit. See sources and related links below for bulb information. Sometimes the license plate and/or the trailer hitch is wired into other circuits and can cause issues in other areas. Sometimes its wires grounding out somewhere on the vehicle. See sources and related links below for bulb information. See owner's manual for location and identification of fuses.