very weird trailer wiring problem

Hi everyone - first post to this Exploder forum, and its a long sordid tale.

I have a 1997 XLT, 4.0L SOHC. I tow a trailer pretty often. I have a factory wiring adapter inserted in the factory location on the rear harness on the truck, and had no trouble with the trailer lights on any trailer UNTIL...one day the trailer lights just didn't work. NONE of them. I have always used dielectric grease at all connections.

I started by checking the trailer lights for loose/corroded/bare wiring or ground problems, but found nothing. Then i checked for power at the truck to trailer 4-pin flat plug, and got nothing. Then I checked for power where the trailer adapter harness plugs into the truck harness above the bumper- water poured out of the trailer adapter harness when I moved it, but there was no power at the truck harness anyway.

I pulled out the manual and checked the approrpriate fuse, which was good. Moreover, the Haynes wiring diagram shows that the license plate lights on the truck and the trailer harness are powered thru the same circuit AND THE LICENSE PLATE LIGHTS WORK!!!

I pulled the bumper cover and looked for loose, shorted or corroded wires in the harness (the bumper got pushed a little a few weeks before trailer lights stopped working) but found no problems. I then pulled apart the connector inside the 1/4 panel behind the jack (outside of truck). Got power to plate lights but nothing to any trailer pin. I wiggled the harness inside the jack storage compartment but got nothing.

I AM CONFUSED! :banghead:

I HAVE to haul the trailer for my business, and the load that I drive with means no one can see the truck lights - not even the 3rd brakelight. This is not a good situation. :uhoh:

The only thing I can think of is to buy and wire in a universal wiring kit, which is a pain and still doesn't guarantee that I'll solve the problem.

Any thoughts are appreciated.

Thanks,

-Keith

Perhaps the factory installed power source for your trailer isn't correct?

Perhaps the factory installed power source for your trailer isn't correct?

Thanks, but I'm still confused. What power source? The trailer doesn't have brakes or anything - its just a utility trailer with a 4-pin lighting harness. If I fried something in the truck's main harness due to a mismatch between truck and trailer, I'd have thought it would have fried in the first year and a half of running the trailer? If that's a silly assumption please forgive me - I'm still working on todays first Mtn Dew.

Also, I just ordered a factory tech CD off Ebay to help with this. I've been using the Haynes manual wiring diagrams which don't seem to be giving me the whole picture of how the trailer pin functions get from the truck to the plug.

Well I don't have the wireing schematic in front of me, but I believe your vehicle has a dedicated trailer-tow ckt with a independent power source from the other external lighting. Most Ford trucks do! Check for a blown fuse in the distribution block under the hood. Just a hunche! I'll look up a diagram at work to be more informed tommorrow if I'm mistaken.

Well I don't have the wireing schematic in front of me, but I believe your vehicle has a dedicated trailer-tow ckt with a independent power source from the other external lighting. Most Ford trucks do! Check for a blown fuse in the distribution block under the hood. Just a hunche! I'll look up a diagram at work to be more informed tommorrow if I'm mistaken.

Thanks! I'll check those fues today. If you do run across a diagram with more info, that would be great also.

Thanks! I'll check those fues today. If you do run across a diagram with more info, that would be great also.


Ok...I feel REALLY stupid. The main trailer power fuse in the D-box was blown. :bricks1: I look under the hood on a regular basis and forgot that box was even there...duh. Sorry to waste time...but I appreciate your taking the time to revisit the obvious...sometimes that's just what's needed.

Your Welcome! :biggrin:

Thanks for posting back!