They make so many different sockets with different retention designs when you twist to lock them. Did your guy just take the tail lamp to the store to find one that fit or is there a specific make/model that it was designed for? I can't tell them I need a 3157 socket for a Tahoe Hybrid since their isn't one used on the car.

 

Actually I had this done by the guy who was doing my retrofit at the time, so we just cut out a couple of turn signal/park light sockets from the front harnesses which I didn't need any more for my retroed headlight configuration.

 

Aha. So you used the front turn signal sockets. Good to know. Thanks.