Unfortunately didn't get a chance to work on it last night. Hoping to find the schematics for the CJB and trace the problem with the multimeter and test light tonight. I'll post what I find.

Bob
2002 F250

 

I'm also having a problem similar to Bob except mine is a little different. My running lights stay lit all the time. I too have check all plug & pins, both trailer & truck side. To the best of my very limited knowledge on this - all check as they should. I have also checked all related fuses which check fine also.

I have an '03 F250 and all fuses are inside the cab (I think).

Any suggestions?

Thanks! Donald

 

The problem was the relay, not the fuse. I took the truck to an automotive electrical shop and, based on what I've read in this and other forums, told them to bypass the stock/internal relay, and install an external relay to control the trailer lights. The cost was reasonable and the problem was solved. The installation of the external relay is neat and clean with it mounted (at any convenient location) under the dash. (I should have just done it myself)

I read that the stock relay that controls the trailer lights in under rated, and that this is a common problem with these trucks. I was also told that the stock relay is molded into the fuse box and can not be replaced (within reason). By bypassing the stock relay and wiring in an external relay, I was able to select one rated for higher current that will probably will never fail again. If it does, it will be simple and inexpensive to replace.

When the stock relay burns out, I believe it can be stuck in either the open (trailer lights always off) or closed position (trailer lights always on).

Hope this helps!

Bob
2002 Ford F250
7.3 Turbo Diesel
Lariat Crew Cab