Were is fuse for trailer running lights ford f250 2006

if you have running lights on the towing vehicle but not in the trailer then the problem will be in the plug of the vehicle as evidenced by the lights working on another car

As trailer lights are run off the existing wiring of the vehicle then those vehicle fuses control the wires and circuits for the trailer. If you have a problem with trailer lights then check the wires and connections in the trailer plugs.

did you check the trailer /tow fuse under hood in truck? located lfet side rear near firewall top. should be fuse for towing / trailer.DW Mylin

The fuses for the trailer tow adapter are in the normal fuse panels.

Engine Compartment fuse panel
101 - Is the battery charge circuit ( hot in run position )
20 - Left Stop / Turn fuse
19 - Right Stop / Turn
5 - Trailer tow reversing lamps & Trailer Tow parking lamps

Cab Fuse Panel
23 - fuse for the relay for the trailer tow battery charge circuit

All of these are in the owners manual

If you did not get an owners manual with your truck ( purchased used ), you can download one from Ford :
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

Did you check the fuse for the trailer tow adapter paring lamps ? This is a separate fuse powered by a relay, it is not the same circuit as the truck's parking lamps.
This is fuse # F10 & The half size ISO relay, R201 in the fuse panel in the passenger side kick panel.
This is based upon being a new body style 2004, not the 2004 Heritage or Lightning models, those are different fuse & relay locations.

There are a few fuses for the trailer tow adapter.

1st, is theodd location on the 97-98, engine mini fuse panel has a 20 A fuse forthe stop / turn lamps. Have seen it covered in tape from the factory onsome 97-98 MY trucks.
This is on page 142 in the owners 1997 manual, all the revisions for the 1998 owners manual I have seen do not include this fuse box for some reason.

Download a PDF version from Ford, for the 1997 MY at :

https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

This is a picture of the Power Distribution Box, additional relay box and engine mini fuse panel with the covers off. The 20A in the upper right panel with the red base, is the trailer stop/turn fuse.


The others :
1. Power Distribution Panel / engine compartment fuse panel
Fuse #1 - Trailer tow back-up and tail lamps
Fuse #16 - Trailer tow battery charge and stop/turn lamps
Fuse #28 - Trailer tow electronic brake

2. Instrument Panel Fuses ( cab fuse panel by hood release )
#23 - trailer tow battery charge relay

if it only happens when the trailer is plugged in you have a short in the trailer. wiring or the bulbs have corrosion or water in the connetor. Same thing if the trailer is unplugged. Check the truck lights

My 2004 f150 has the factory tow package. It has a fuse for the trailer running lights seperate from the truck running light fuse.
Check, you may have the same set up...

The fuses and relays for the trailer are isolated from the regular running lights, I believe the fuses and relays are in the underhood power ditribution box.