My right rear brake light keeps burning out. I discovered that this is because there is a loose interior lens that keeps falling on the bulb. I went to replace the entire housing but its completely different than mine. I have those twist out no wire bulb holders and all the replacements I'm finding are wired in series.

That's not a big deal except I have a 4th bulb in the right rear tail light. It has a standard bulb (round socket), it does not appear to be tap'd into the leads. Any ideas what this is? I was thinking maybe its a splice for the trailer lights but now I'm not so sure. I can easily re-install it in the new tail light housing but if its junk I'd rather get rid of it... If it wasn't 12 degrees outside I could start ripping her open