Sounds like you have a disconnected ground wire. Open the trunk, pull back the upholstery and find the wiring harness that leads to the lights. In the wiring harness, there should be a black wire with the bunch. That is the ground wire. Trace that wire in both directions to see if you find a break or disconnection. The wire usually bolts to some sheet metal somewhere inside the trunk and the grounding point is usually identified with the use of a green painted screw holding the wire to the sheet metal.