please help

A lot of the time the sockets get corroded and the bottom center contact for the bulb loses its "springyness". It's really very simple. You need power and a good ground. Sometimes also, painted surfaces provide a poor ground. Make up a alligator-clip jumper wire and connect one end to a really good unpainted ground back there in the trunk area (maybe under the bumper). Then clip the other end on the sockets to provide a ground.