Trailer lights fuse

[Fergie]

This thing is driving me to drink more! Last night it was blowing fairly quick while park. Since I fiddled with things after that it now only blows going down the road. Following a local farm mechanic's advice I put an 20 amp inline fuse on the brown wire on trailer plug. Maybe it won't work but the theory is if it's the trailer it'll blow the 20 amp if it's the tractor the 30 amp will blow. Of course I hooked that up and lights stayed on for 20 minutes and I was wiggling wires on the truck during the this time. Find out in the morning I guess hopefully it'll be a starting point.