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What do you mean when you say you "messed" with the UVC wiring harness? Most here will agree that your problem is the UVC wiring harness. Not the IDM.
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I agree. If it were me, I'd invest in two new UVC harnesses from International for $50 or less, and maybe even new VC gaskets. I'd also thoroughly check the wiring for shorts/opens. All this before I dropped $500 on an IDM that may not fix the problem.
BUT FIRST, I'd get the codes from the IDM to tell me where to look. Like I've said before, the P1316 never comes alone, it mainly says pull the codes from the IDM to see what's up.