no signal or brake lights-intermittently 2000 f150 4x4
 

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

Welcome to the forum....and the dark side ;)

When you replaced the multifunction switch did you take a look at the connectors on it? The wires pull out of the hardshells quite regularly, especially if it has tilt.
These trucks do suffer sometimes from water getting into the under dash fuse box and GEM (Generic Electronic Module) which is attached to the back of the fuse box. Usually the water gets in there from a leaking windshield. Your symptoms aren't common for this problem but anything is possible. The common symptoms for that problem are the heater won't turn off with the key out and things like that.
You said you checked the trailer wiring. Have you tried removing the trailer harness from the system and see if that changes anything? I've been fooled by bad trailer harnesses and plugs before.

Thanks Dave For The Advice- I Believe The Problem Was Contacts Sticking In My Turn Signal /hazard Flasher. Replaced It - So Far So Good . Ive Neber Really Heard Of This For A Blowing Fuse Concern But Like You Said Anything Is Possible. Sorry This Is So Long In Returning I Went Down To Montans For A Small Vacation - Truck Ran Great All The Way.mobil One Oil For 19.99 For Five Quarts . Cdn Equivalent Probably 44+ Dollars. Thanks Again . If You Ever Need G.m. Help I'm Here. Murray A.k.a Mr. Big !

ARE YOU TALKING ABOUT THE CONTACTS IN THE FUSE BOX OR IN THE COLUMN?