Tracked down a problem I have on my old car ( this is not the mustang) rear tail lights work bit the LR trun signal does not. Has the correct 1157 bulb. Pulling the bulb and using a test light on the contact it gets its power fine and the test light blinks as the bulb should but i have tried several new 1157 bulbs and none will work. I assume something wrong with the socket? I would say the ground is fine since the tail lights work. Any advice or a fix????