No trailer lights

It looks like dielectric grease, which should be there, but it looks filthy.

If that were my plug ........I would kill any power to it, wipe all possible with a rag, put my safety glasses on, and blast the hell out of it with CRC electronic cleaner (any parts store), then with an air line blow nozzle.

Repeat if necessary, until you can clearly see the connector housing, as well as the inside of each of those plug holes to be shining just as you see the few tips shine in that picture.

Once that is done, check the lights. If that was the issue, reapply dielectric grease (any parts store) and get on the road.

Above all else .......do not try what post #3 said, that's just whack!

 

Go to walmart and buy some adhesive LED light strips. It will do the job, just swap batteries until you fix them.

 

All that black mess looks like corrosion from something grounding out and backfeeding. Don't listen to that poster above. Don't go jumping terminals if you don't know what you're doing. Check all your fuses and if they're good take it to a shop.