I am purchasing a 2002 F250 XLT Quad cab 7.3 diesel 4x4 with 115K. It was in to the dealer at 100k for maintenance, but I am wondering what maint. It may now need asde from lube?

Question corrected for clarity.

The Passenger Compartment (steering wheel) box does 2002 to 2007 according to these. HOWEVER, although the same layout, so do different things depending on the year like this one.

Fuse8 15amp 2003-2004, Diesel: Back-up lamps 20amp 2005-2007: Back-up lamps

Ford F-350 (2002 - 2007) - fuse box diagram - Auto Genius

https://www.autogenius.info > ford-f-350-2002-2007-f...
May 17, 2018 - Ford F-350 (2002 - 2007) - fuse box diagram. Year of production: 2002, 2003, 2004, 2005, 2006, 2007. Passenger Compartment Fuse Box.

Ford F-250 / F-350 / F-450 / F-550 (2000-2003) fuses and ...

https://fuse-box.info > ford > ford-f-250-f-350-f-450-f-...
Fuse box diagram (location and assignment of electrical fuses and relays) for Ford F-series Super Duty (F250 / F350 / F450 / F550) (2000, 2001, 2002, 2003).

More here
https://www.google.com/search?q=2002+ford+f-350+diesel+7.3.+xlt+super+duty+fuse+box+diagram

Relay or control module?

Motorcraft Glow Plug Relay 7 3 PowerStroke DI Turbo Diesel

Motorcraft Glow Plug Control Module

Most manufactures recommend changing a timing belt at 100k but I've seen them go several hundred thousand miles and no problem. I've also seen them break under 100k. The best maintenance is preventative maintenance or fixing things before they become a problem. I would recommend replacing it if you have the means to do so as you will also be replacing the water pump which is driven off the timing belt (do them together)..

Fuel capacity is 38 galons.
Found it on:
http://consumerguideauto.howstuffworks.com/2002-ford-f-250-f-350-super-duty-13.htm

I would suspect the turn signal switch, turn the left turn signals on and grab the knob for the hazard switch and tug and push on it, if they start to work, the turn signal switch is bad.

not sure here as this is an american vehicle with a bigger engine than a ten ton truck here in spain ,but the newer fords will not run if petrol is put in as their is some sort of sensor that shuts the immobilisor down so it will not start ,again another dealer only job---- to release the immobilisor .if you not sure take a pipe off and have a smell

you should be able to tow it with the transfer case in the nuetral position.

I was wanting to know if i could just buy a pair of f250 towing mirrors and would they fit or match up with my 2002 f150 single cab?

Your brake master cylinder is faulty.

ARE YOU SURE THE CODE IS P2262. AND "We just recently moved from Indiana to Arizona pulling a large 5th Wheel. I am wondering if that is contributing to the issue" NOT REALLY. IT ALL DEPENDS ON HOW THE TRUCK WAS DRIVEN..DID IT SIT A LOT AND/OR WAS IT BABIED. MORE THAN LIKELY YOUR TURBO IS EITHER FULL OF CARBON OR RUSTED. THE TURBO CAN BE CLEANED, UNLESS OF VISIBLE DAMAGE. IT CAN ALSO STILL BE UNDER WARRANTY AND THATS IF YOU HAVE LESS THAN 100K MILES AND WHEN YOUR WARANTY START DATE IS. THERE IS A 5 YEAR/100K MILE WARANTY ON THE POWERTRAIN.

IF YOU HAVE ANY MORE QUESTIONS ASK AWAY.