I've got a 2001 Dodge Cummins and have been battling the electrical gremlins for the last few months. This seems to be a common theme for Dodge truck owners.
Most of the fixes I've seen (and have resolved on my own) come from pulling apart each connector, and removing each wire from the connector plugs. If they're fairly clean, add some flux and solder the pin to the wire; it seems the crimp isn't quite enough over time. Do this one at a time for each connector plug, so you don't get things crossed around.
Once everything is soldered & cleaned up, use some di-electric grease on each connection to keep corrosion at bay for awhile.
Sometimes I need to take a hard eraser (like we used to use in school way back when) to clean the contacts on each fuse, to resolve issues like you are currently having. And the previous poster is exactly right about the rear wiring harness, get that thing cleaned up first...I'd solder each connection and double heat-shrink them for the best protection. If you live in a wet/humid environment, or experience snow in the winter on a regular basis, most likely your electrical connections are green & crusty by now and may even be in need of replacement. I highly recommend Geno's Garage (
http://www.genosgarage.com) and the Turbo Diesel Register (
http://www.turbodieselregister.com/) for help with any Dodge Cummins issues....I've been able to solve many a problem with my truck with help from the TDR and Geno's.