[updated:LAST EDITED ON 06-Nov-02 AT 09:13 PM (EST)]Hi,

Im new here and looking for help with the trailer lights on my truck. It's the truck I drive for work, a 1998 F-150 XL with a 4.2 v6. It has the factory tow package and had a 7-pin connector for trailer lights (now it's a 4-pin, read on). They've been working fine until a few weeks ago. I hadn't towed a trailer in about a week, and when I hooked up the trailer pigtail to the truck, I only had parking lights, no brakes or turn signals.

I was using a 7-pin to 4-pin adapter in the truck's plug (our trailer doesn't have brakes), and tried a new one of those. No change. Then I cut off the 7-pin connector and wired a 4-pin connector to the existing brake/park/turn/ground wires. No change. Then I bought a 4-pin trailer light adapter that plugs directly in to the wiring harness connector at the rear drivers side. I had the same result. No brake/turns, only parking lights at the new trailer light connector. All the fuses I can find have been checked (under the dash and under the hood) and none are blown. The relays all work, too. The problem is also not with the trailer, as all the trailer lights work correctly when hooked to any other of my bosses trucks.

All the lights on the truck work correctly, it's just the trailer lights that are affected. I really would appreciate some help...I tow a trailer a lot. Is there a fuse hidden somewhere that I haven't found? Has anyone else had this problem?

TIA,
Dave
Palm Bay, FL

 

Have you used a 12V test light to verify power availability at all pins on the truck plug? You may need a helper to step on the brakes, shift the truck into reverse, etc. Buy contact cleaner and clean all contacts.

Is the plug as installed by Ford, or done aftermarket? Loose or misrouted wiring?

 

>Have you used a 12V test light to verify power availability
>at all pins on the truck plug? You may need a helper to step
>on the brakes, shift the truck into reverse, etc. Buy
>contact cleaner and clean all contacts.
>
>Is the plug as installed by Ford, or done aftermarket? Loose
>or misrouted wiring?

Done, done, and done. My boss and I have tried everthing we can think of, and double and triple checked everything. The plug is a factory wired trailer light harness. The wires are all bundled with the factory taillight harness and included in the factory wiring harness plugs. There are separate wires in the bundle for the truck tail/stop lights and the trailer lights. The truck lights work fine, trailer has no stop/turns.

The only thing I can think of is that there is a hidden fuse or relay somewhere that we can't find. The lights worked fine for four years and then just quit. We did find one fuse under the hood, on our initial check, that was blown. One of those tiny ones, a twenty amp, and it's been replaced and hasn't blown again.

This is very frustrating. I'm hoping to not have to rewire the trailer harness, but that may be what has to be done. Does anyone have a breakdown of the tail/brake light wire colors (for the truck, not the trailer)?

Thanks for the help,

Dave

 

With the left or right turn signal on, should be able to hear the respective left or right trailer tow turn relay click-clack under the hood. I think both the trailer tow turn relays close for stop.
Trailer left side is Yellow coming from its relay to rear connector. Trailer right side is Dark Green doing the same on its side.

 

dave,
i had a similar problem with my factory tow light kit. ironically enough i overlooked a small fuse box located in the engine compartment. on the drivers side under the fender is a small fuse box. 1 inch by 4 inch. they're are about 6-8 fuses here. start here. good luck
tom

 

I had the same issue and also found the solution in the fuse box mentioned in the post just previous to mine. Check there!
Greg

 

Yes, it was that small fusebox. There were spaces for six fuses, only two installed, a five amp and a twenty amp. The twenty amp was blown; replaced it and the lights work! Why is this fuse block not documented in the owners manual? Or the relay block next to it? Interesting...

Thanks for the help guys!

You saved me a lot of time and headache!

Dave

 

I had the same problem. That fuse box is not in any of my manuals. Thanks for the help.

 

 

Just worked on one with both turn relays burned out. (no brake or turn signals on the trailer, truck worked fine) Both clicked but did not work. Relay box was attached to main under hood fuse box. This box is not shown in owners manual. Your looking for the two small rectangular relays closest to the engine, they sit side by side. Not to be confused with the small box with the 5amp and 20amp fuse shown in the manual. This box sits where the manual shows the smaller box is mounted. Who would think both relays would be bad?
Tim

 

ok so I am no fixer upper lol but have you tried to hook up any other trailer at all to see if the lights work on that one. My boat trailer kicks my *** all the time yet my car trailer no issue at all I guess if I got stuck under water 3-5 times a week I might not want to work either lol good luck

 

I had the same problem. It was the fuse under the hood

 

i have that same box and have for days on end tryed to figure out what it was now i know but still no documentation as to whats what? inside? id realy like to know where to get documentation?

Also i have a question maby someone can answer?
if the drivers side relay is bad could that short out my drivers side brake light and drivers side turn signal?

 

Any one have a pic or better explination on where the small fuse box is? I have a 1998 F250 that the right turn (& brake on the right side) for the trailers is not working, have no blown fuses in the power distribution box under the hood or the fuse panel in the lower left of the dash. Thanks

Toby