Prostar tailights

Ok, I think there is a "Y" butt connection from the main harness at the back near the lights where it splits into two connectors, one for each light. This butt connection might be bad. If the power is fine, I guess you need new lights.

 

Yes, they are a body controller output, but I highly doubt you have a bad bc. The body controller only has one power output for those lights, so if you are having the tail lights do different things at the same time then it is still wiring or the lights themselves. Worrying about or even replacing a body controller for an issue like this is your dead-last option!

 

It will be buried inside the loom.