On a '06 SD 350 with tow package, I have no current on my 7 way or 4 way for running lights. I checked the fuse #38 20 amp and it's OK. Even swapped it for another and OK. Everything else is OK, brakes, directionals. I thought it was the trailer but when I tried the 4 way with a 4 way tester and a tester on the 7 way it wasn't. I'm getting ready for a trip very soon ( hours) and now this. I'm not the greatest electrical wizard so any help

 

I had the same problem. turned out to be a seperate fuse for the running lights.

 

Would that be #38? It says trailer parking lights. They came on when I hooked it up but moved it a few feet and shut off. I thought it was the trailer but ended up on the truck.

Is there a relay for them?

 

I don't know the fuse number, but there is a yellowish (don't remember the wattage) fuse under the hood in a block on the driver's side of the engine bay that may be your problem.

 

Fuse panel lower left of the steering column

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The fuse list # 38 is your running /park lights for the trailer.
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Online owners manual; https://www.fleet.ford.com/maintenan...ls/results.asp

Sounds like a short in the trailer wiring is blowing the fuse in the truck.

 

This. Finding the short is the fun part.

 

OK I reread the op.
The fuse is good!
Do the other circuits work?
Do you have turn signals/ Brake lights when the running lights are inop?
If the fuse is good then you need to look to the ground circuit.
Time to break out the test light and Ohm Meter.
You need to do a check to find where the current fails to reach ground.
If you have current to the light but it still does not work the ground is the problem.

 

I have everything but running lights. Rechecked the fuse #38 before my little trip and all is fine. I'm not sure if there is one under the hood as was posted. None is listed in the diagram that I can see. I'm just trying to see if I'm missing a fuse or relay before poking around. I'm going to start at the plug behind it and see if I have current before it. I hope it's there with some corrosion on the plug. My electrical trouble shooting experience is small but my determination not to have to pay to have this fixed is great.

I don't believe it's the horse trailer. I hooked up another vehicle to it and no problems.

 

"Running" = "park" lamps.

 

OK everything works when hooked up to a different vehicle.
That puts the problem in the first truck.
You need to probe with a test light checking the circuit.
Make sure that you have power into the fuse then outward from there.
Follow the harness and probe each connector for power.
Try the electrical forum to see if someone has the wiring diagrams for your truck.
A emergency fix would be to run a fused wire from the battery through a switch under the truck back to the trailer plug.
I would use at least a 12 gauge wire for incandescent bulbs.