hi everyone-im a licensed g.m. tech and have worked on all models of cars througnout my career.i have had the truck for the last 5 years no major issues at all.year and a half ago 20 amp break fuse popped in wet conditions. Traced it back to a faulty Multi function switch. replaced with used switch no problems until june 07. Same fuse popped, installed new fuse, pops immediately, installed new multi function switch, still no brake or tail lights. Happened again in wet contditions, never happens when vehicle is in use, only after being parked. Installed short locater. Could not see any chaffed wired, no corrosion in any plugs on frame, checked trailer wiring (does not pull trailer). Installed new 20 amp fuse. Was ok until today. Have I over looked anything? Anyone experience this? Checked complete wiring harness from trailer plug to UHFB. Ford couldn't help, said nothing wrong. Slight moisture here Thursday, possibly contributing to condition. Working fine now, please, please please any ideas would help me at all. Truck in garage only 80K.

Signed frustrated