I also have a 91 YJ 4.0 and have completely swapped columns out from another jeep. I never ran into any wiring problems, does your replacement harness require you to splice things up rather than a plug and play kinda setup? I would be happy to look at my jeep if you can tell me what exactly you need to know.
Edit: Also from my experience from junk yard hunting and such the '91 seemed to be the bastard child of wiring with the 87-90 models have one kind dash wiring, and the 92+ jeeps having another. For instance the center five gauges as far as i have found can ONLY come from another '91 to plug right up, all the models i have checked from other years used slightly different gauges with slightly different plugs.
91 wrangler 4.0L, 4 in Suspension lift, 1 inch Shackle Lift, 1 inch Body Lift, 35" BFG Mud Terrains, Warn Rockcrawler Front Bumper, Hand Throttle, HiLift, 12 pack of Natty Boh.