Lighting on trailer

I ran a wire from the bottom left screw of the brake light to a bolt on the frame and everything works now. Thanks for the help.

I would if I was positive that would fix this issue. I also spent 28 dollars on the adapter to go from 6 square to four flat. The only reason that I see changing the trailer plug would be if the adapter was at fault.

I remember my dad dealing with this when I was younger. His solution was to put a new 4 flat connector on the trailer side so that it would be easier and more convenient than dealing with the 6 pin square connector that never seemed to stay in place.

If you want to go that route here is a helpful link

Did you check that is continuity between the green wire and the white wire?

Yes, you can run a separate ground to a known good ground or the chassis frame, won't hurt a thing.

Also after inspecting the lights they look fine. Could I run a new wire from the ground on the lights and just mount it to a bolt on the trailer frame?

OK I ran a wire from the negative battery terminal on the Trailer to the brake lights and they worked with the headlights on. So what do I need to do for a permanent fix?

Sounds like a grounding problem. The brake lights are grounding through the headlight circuit and turning the lights on kills the ground. My guess though is it's not the headlights themselves that are killing the ground. I'll bet it happens if you just turn on the running lights but leave the headlights off.

First thing I would do is grab a long wire or a set of battery jumper cables. Temporarily connect a ground wire from the trailer to the tow vehicle and see if all the lights work.

Next pull the bulbs out of the taillight housing and inspect them. Do they both have a dual filament or did somebody force a single filament bulb into the socket? Inspect the sockets and housing and make sure they aren't melted and the contacts in the socket are free to move and spring back if you push them.

If there is a ground connection in either light housing then make sure it's tight. Try running a separate ground from the outside of the light socket to a ground on the trailer. See if the lights now work with the headlights on.

Do the running lights work correctly?