MustangSteve’s HOW TO REPAIR WORN OUT TAIL LIGHT SOCKETS in a 65-66 Mustang
There is no reason to have to replace an entire taillight housing if the bulb socket or wire connections are bad. A $3.99 part from Pep Boys will allow you to replace the socket. This new socket also will allow you to be able to access the bulb for future replacement simply by unsnapping the socket from the enlarged hole in the housing, making it possible to change bulbs with no tools from inside the trunk.
This is the part to buy. It even comes with the connectors.
Existing socket shown as viewed from inside the trunk. Use a cut off wheel and remove the brass socket.
Existing socket shown as viewed from the light fixture. This socket must be removed completely. Once removed, enlarge the hole so the new socket just tightly snaps in place. The new hole should be about 1" in diameter. It is suggested that you measure the actual receptacle you buy to be sure you get the right size hole. I used a 3/8" diameter carbide bit in my die grinder to carefully enlarge the hole.
This is the new socket shown from the rear. After snapping mine in place, I bent the six tangs out tight against the housing to hold it in place securely. If you are careful and get the hole size just right, the socket will snap right in place and will not need the tangs bent over.
Here is the view of the new socket from the trunk. There are two wires to reconnect. Temporarily stick your existing wires into the two new connectors and turn on the car's headlights. One of the bulb filaments should light up. Now, turn on the turn signal. If the turn signal appears brighter than the running light, you have the wires correct, so be sure they are properly inserted and then crimp the fasteners. If the turn signal flasher is not as bright as the running light, reverse the two wires and recheck. The turn signal should be brighter than the running lights.
That is all there is to it!