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.