Thank you for this post! Last night, what I did was took out the base and switched the contacts on those two but that did not work. Tonight, I will try and pry the top part which is the circuit board like what you said and switch the + and -. I'm just a little iffy about popping off the top part because I might break something in there.
By the way, there is what I bought and I'm planning on putting all these in my tail lights.
10 x White 1156 BA15S LED 27 SMD Light Bulbs Tail Backup RV camper 1141 1003 | eBay