I've never had a trailer that didn't need a full wiring re-do after about 4-5 years. They are wired at the factory so quickly and cheaply it's a wonder they last that long. You'll find wires stapled to the wood floors, run thru torch cut holes, drilled holes (raw edges), un-insulated butt connectors, even household marretts. Personally I would look at the overall condition of the wiring under the trailer and if nothing obvious grabs your attention you can do a complete re-do in the same amount of time it takes to search out the issue.
Do it once and do it right.
Sealed 7 pin junction box up front on the tongue so you can replace the plug and lead as they are the easiest to get damaged
jacketed wire to the back and brakes held in place with cushion clamps. i run a three wire down each side to pick up the tail,stop/turn and ground for that side, and a dedicated two wire for clearance lights and a second dedicated two wire for the brakes. all connect in the junction box and could be replaced individually if ever needed. All ground also come back to the box,(no wiggling of the lights to get them working)
all connections should be covered with adhesive filled shrink wrap for a watertight seal
I also prefer sealed LED's, Never have to change a bulb again.
I just take it as part of trailer ownership that at some time it will need to be re-wired. Hope you sort it out
Ross..
My Rides
1985 250R original (Garage Queen)
-under restoration
1985 250R black and blue full rebuild ( Daily Rider)
-Paul Turner pipe
-+2" Westcoast
1985 Red and White Tecat-EH Sold
1985 Green Tecate Sold
My Wife's Ride
-2003 Suzuki LTZ 400 Showroom fresh and completely stock
My Kids Ride
-2004 Yamaha Blaster, Completely Stock
-2006 Yamaha Blaster, Completely Stock