Re: 2002 7.3l
Electrical issues are almost always hard to pinpoint even with the proper equipment to help diagnose. Have you owned it for more than a year? The reason I ask is that some newer diesels won't allow any accessories to run without the engine running because in cold weather the glow plugs take a bit of energy to warm up the air intake charge before you can start the engine. Turning to accessory mode (turn the key back towards you) should allow you to run accessories without the delay.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!