How did this happen?

Depending how they are wired the side turn signals only blink or both blink and come on with brake lights. They are not normally a marker light.

 

Yea ive done that a few times. Tight nearly touching trailer with ferring turns (no choice on some of these tight as hell dump sites) and the line gets snagged then rip goes said line. They are pretty cheap so i always carry spares and spare sockets. Just replace it, shut up, and roll imo. Also id ensure you have enough flex in the hangars. I typically hang them so there is about a finger width between my deck and line and get the longer lines beside. Happens less that way.