For a while now I’d been having trouble with the 4-wheel drive shifting on my Dodge Ram 2500 pickup truck. I would select to shift to 4-wheel drive, and the shift would start but never complete. At least once I found the truck in 4WD without asking for it, and often I would get a warning message about a malfunction.
Last winter I traced the problem to damage somewhere in the wiring harness so I ran a temporary wire to cure it.
Now that the weather is nicer I repaired the harness properly. I had to do this anyway because another wire had failed and the shifting again did not work.
I managed to expose the harness and repair the wires, which seemed to have been damaged just by chafing against another surface. I had suspected rodent damage but I saw no tooth marks in the damaged area of the harness. I repaired the broken wires, re-sheathed the harness, and got it all back in place and working, all detailed in this YouTube video.
I never did figure out how the harness was damaged in the first place.
Now I have a nearly-new shifter motor and Drive Train Control Module (DTCM) which I had tried installing during the winter to cure the problem, and no use for them. Maybe I’ll try selling them on eBay.