Trailer tail light staying on

[archie18]

I had to replace the 7pin connector on my trailer that connects to the tow vehicle. Everything works fine when connected to the tow vehicle (2014 F-150) but when I disconnect the trailer and go on battery power the right tail light on the trailer stays on. Any suggestions for troubleshooting this other than redoing the plug?

[Mandalay_Parr]

A good rule of troubleshooting is to go back to last place you were.
And, that was the plug.

[wnjj]

Take the plug apart. You likely have a couple strands of wire shorting between the right brake light and the +12V pin which are next to each other. Plugging into the truck may cause the pins to move enough so the strands no longer touch inside the plug.

[RJsfishin]

If it didn't do it before, I would have to suspect the hot 12v charging wire
short circuiting to the taillite wire.