If you have manual locking hubs they lock when you turn clockwise. This engages the wheels to the front axles and the front differential. You can then engage the 4wd from the cab lever. If you unlock the hubs (turn couterclockwise) they disengage and "free wheel" This position saves a little fuel since you are not spinning all that heavy steel in the front differential all the time. You should always engge the hubs a few times per year even if you don't use the 4wd. This allows all of the oil seals to turn and get new lubricant.
To the right of the gas pedal, behind the center consol.
The 2003 Ford f250 did not come with an air cabin filter. There was a dealer install option but very few were ever put in.
behind or under back seat
Yes they will. As long as it is an f-250 or greater and the a 150. 99-07 are the same pattern. early 99's are different.
1994-2003
They should both be 8x170mm IIRC, so yes. The older ones, pre 96 I think, had 8x6.8" IIRC.
Diesels do not use oxygen sensors
I know that the 2003 ford f250 diesel was what they call the lemon year. They swiched from a 7.3 to 6.0
Tail lights and brake lights fuse.
he drives a Ford f250
A 2003 Ford F-250 column gear shifter can be fixed by simply tightening it again. You can tighten it by turning the adjustment wheel on the lower right side of the steering column.
http://www.acrobatfiles.com/result-97-ford-f250-parts-diagram.html This site covers all years plus they have an "ask the mechanic" service.