Blame yourself for not looking into the problem 20k miles ago when it first started.
I hate to say it, but this, right here, is the best answer I've seen.
I get it, we all get busy, and sometimes I'm the absolute king of procrastination. However, this is a serious thing, especially on a truck that you use as a daily driver. Maybe I'm more sensitive to it than most given my remote location (where for me, getting stuck means *at least* a 10-20 mile walk home, no cell signal half the time to call the wife or anyone for a pick-up, and no taxi or uber to call. Don't ask what towing would cost out here.)
Either way, letting something slide even if it looks minor is definitely not something you should do on a daily driver, no matter what you drive (truck, car, motorbike, scooter... doesn't matter. Fix that **** ASAP if you can, doubly so if you're still paying on the thing.)
If all else fails, scrounge through the junkyards for replacements on suspect parts, load the Parts Cannon, and fire at will. Speaking of which, I bet that with a bit of sweat and a handful of tools you could get a new (okay, working) harness yourself out of a wrecked junkyard RAM, and do it for less than an hour's work and maybe $50 max. Those things are quite modular, and the RAM 4th Gen covers a whole lotta years. The odds of a perfect fit if you slop it +/- 1 or 2 model years in either direction? Pretty solid odds worth chasing, and if it were me having to do it, I'd go for that.
Seriously though - the problem should have been looked at at the first sign of something wrong. If nothing else, see if you can find the issue yourself, or get a dealer or mechanic to troubleshoot it for you, then politely refuse whatever it is they say needs repaired (basically "Wow... I don't quite have the money for that. Can I get back to you?", then take it home, double-check if you can, and do the fixing part yourself if you have the skills to do so.)
PS: did you get a Carfax report before you bought it? Hindsight and all that ****, but I am curious. I ask because if you got a clean Carfax for it but there's obvious signs of, say, flood damage, you might get some help out of that direction.