Trailer light problems

You have a bad socket some where. Probably full of water. Stay out of the wiring and the fuse box. Start with tractor tail lights. Don't start rewiring it's something simple.

 

Ok so your title says trailer light problems but you don't mention if this problem occurs with or without the trailer hooked up. If it only does it with the trailer hooked up the problem is most likely in the trailer.

 

Your ground on the trailer isn't making contact. If you can spread it gently with a flathead then do it.

 

You most likely have a bad ground. I have also seen corrosion in connections for the trailer lights and turn signal lights back feed from corrosion. Used to take me days to trace this crap down, but I bought this lead set called a load pro, and it actually works. You could make one, but I am too lazy. just load the circuit, and you will find your corrosion easily by the voltage drop.

 

I usually just use a my Fluke multimeter. Hasn't failed me yet.