For some unknown reason, there was a "left" and a "right" in stoplight switches. It may have had something to do with the model year or the style of the truck OR the cars may have used the opposite style than the trucks OR you may have to mount it "upside-down. I ran into that once but I can't remember what I did to fix the problem. I think I took it back to the Chev dealer and got the right one. Its been a long,long time ago. Hope that helps.Bill
