Ford 2008 F350 Super duty, What fuses should be replaced if pigtail only works on blinkers and brakes, no running lights

I am dealing with the same problem. I have a 2006 F250 Diesel and a 2010 F350 Diesel. When we hook the trailer up to both trucks the break lights, turn lights and hazard lights work, but no running lights. Running lights on the truck work fine. Here is where to start and finally what it could end up being. Check all fuses: Ours were good. Test the wires back at the light and see if you get a positive reading. Do the same at the plug and the truck plug. All of our wires had good readings. Test the trailer by plugging up to a negative and touching different spots on trailer. if there is a positive reading you have an exposed wire that is not allowing trailer to ground. We ended up buying new lights and rewired the entire trailer. Thinking the running lights may have blown. But with new lights and wires we still did not have running lights You could skip to this step 1st, we hooked the trailer up to a neighbors truck and all lights worked on the trailer. So the problem is something in the ford trucks. Tomorrow we are going to follow the wires frrom the truck plug back to the hood. Was told we need to look for all ground wires and make sure there isnt any corrosion and connections are clean. i will let you know what we find. If you are in a hurry you can do one of these two things. Undo the brown wire from the trailer plug. Keep all other wires as they are and plug into truck. Add a small battery or if you have one, hook the brown wires to the battery. you can run an extra ground from the lights to the negative and add a toggle switch to turn them on and off. Or you can run the brown wires through a switch and to your truck batteries until the problem is found

I meant to put this in. First check the fuse for the Trailer tow park lights. In my truck it is located in the fuse box on the driver side below the steering column dash board. It is number 38 in our fuse box. It was blown when we first checked and added a new one. Ours blew again, which means somewhere our ground is not working.

25 amp mini fuse, In the middle of the power box right beside the little relays that are clicking when the signal is on. the owners manual will point you to the relays but there is a ** that means a mini fuse on the same circuit.

i have a tow truck eagle 450 that when the 4-ways are on the right side does not work. i think even the turn signal does not work either. Where should i start if the fuse and relays check out. could it be a short in the steering coulobm

I have an F350 Power Stroke, when the horse trailer is hooked up the it causes the truck rear blinkers not to work. Last time I took it in I was told it was NOT the bulb, it was a fuse. Which fuse is if? I found some under the hood but it looks like their is another box of fuses by looking at the owners manual. But not sure or where? cant find them under the dash? thought that is were they were. I found some under the hood. But think those are the wrong ones?

When no running lights or clearance lights on trailer or truck I found that my head lamp switch was faulty.