Brand new FTE here, trying to locate underhood fuses for Trailer Plug (left turn/brake lights not working) on 2003 F250 (6.0 Diesel). Was informed yesterday by RV guy that Ford's had separate fuses for trailer plug, that was news to me. Any help? Thanks.

 

You can find the information in your owner's manual. If you don't have one, you can download a copy here.

https://www.fleet.ford.com/maintenan...ls/default.asp

 

Driver side under hood, black looking box. Just open it up.

 

Trying to locate fuses to trailer plug (left turn blinker and left brake light on trailer not working) Truck is 2003 F250 SuperCab with 6.0 Diesel. Truck turn signal and brake light work fine. I have read manual and it does NOT to the best of my knowledge show or tell where the underhood fuses are located. I have two small black plastic boxes underhood, drivers side, one has two fuses and four relays?, the other has two relays? Both fuses were good. Any suggestions? thanks all for views and advice so far.

 

Get a test light check your truck trailer plug.
How To Use a Test Light - Using a Circuit Tester to Troubleshoot Electrical - Ground Check Circuit Test
It sounds like you have a wire problem on the trailer.

 

etrailer.com | Trailer Wiring Diagrams

 

Your owners manual is at...

http://www.motorcraftservice.com/pub.../03f23og5e.pdf

Refer to page 178. The Trailer Tow Stop/Turn Lamp fuse is fuse #6 in the Central Junction Box under the access panel below the steering wheel. It's not under the hood. From what you describe, and based on the fact that the Owner's Manual doesn't describe the under hood fuse box, I'd say that your 2003 is like my 2004 and there is no under hood fuse box. I believe the two fuses and 4 relays have to do with the diesel engine controls, but I'm not sure, they're not described anywhere that I've found. The two relays alone are the 4x4 shift control relays.

 

I've attached a diagram below. Thing is, if only your left turn/stop light aren't working, then I'm assuming your right turn/stop light are. Which means it can't be the fuse, because the fuse is for both left and right.

This means it has to be the relay, or a broken wire. The diagram below shows the turn/stop relays. But be aware, that this is from a 2004 service manual. I can't guarantee that a 2003 is the same.

 

The truck and trailer lights are on parallel circuits fed from the Multi-Function switch so it is common for one to work and the other not to work. Fuse #6 (20A) feeds both the trailer LH turn/brake & RH turn/brake so if one of this is working it can't be a fuse issue. The LH and RH are controlled by separate relays so it could be a relay issue or a wiring issue related to the relay. The relays are in the Relay Block located under the hood. Follow the link below for the schematic.

https://www.fleet.ford.com/truckbbas...bb_pdf/203.pdf

 

Don't buy a new relay until you've swapped the L & R relays. If there is a BAD relay, the problem will switch sides!

 

I have a 2003 ford f250 diesel. The running lights fuse blows when I turn the head lights on. Brake, head lights,turn signals work. Running,park, and dash lights do not. Any ideas?

 

This is an old thread and I have the same problem as was originally posted. Brake and turn lights work fine on truck but not coming back to the trailer plug. I replaced fuse #6 even though it looked good and still nothing. My emergency flasher quit years ago and I haven't been able to find it but all the lights and turns worked great until a couple of weeks ago. I would like to know for sure if there is or is not another fuse box under the hood. I can't find it if there is. I really need this fixed as I only use this truck for towing the trail bronco around and I have places to go. Thanks for any help.