Jeep Cherokee Forum - specific 91 XJ aux/electric cooling fan not working

Please don't hate and apologies for the long post.
I truly have looked high and low via this and other forums and Google.
I can find a pretty good amount of information on Renix cooling systems with the sensor in the radiator. I can also find some useful information on later model OBDII XJ's but those don't quite match up with the 91 and a couple other years (that seem to be a mix of the two systems) aux electric fan troubleshooting.

First of all, I've been a lurker here for awhile and love the info here. This may be my first post, not sure. My XJ has 227K plus, runs great. Over the years have replaced most maintenance things like water pump, radiator, t-stat, hoses, starter, various sensors, intake/exhaust gasket, fuel pump, etc, etc.

I'm usually quite good at troubleshooting but can't seem to get this one figured out.
My aux fan used to rarely come on except in high ambient temps or when A/C was on. It's recently stopped.
I've don't lots of troubleshooting.
Fan runs directly attached to battery.
I've done the mod to the PDC/Aux fan relay with a switch to manually run the fan, works great so I think this rules out the relay (which I've replaced anyway) and the wiring to the fan itself.
When unplugging the temp sensor at the t-stat the fan doesn't come on but I do get a check engine light (pre-odbII) which leaves me to believe that is working fine. I've also jumpered that connection with no results. This is also a new sensor.
I thought maybe it was an issue with low/high A/C coolant pressure. I've jumpered the low pressure sensor connector with no results, I didn't see a high temp sensor.
I've pulled the dash temp control section. Fan blower works in all positions. The baffles (which are vacuum controlled) all work great, each position moves baffles correctly including the MAX A/C baffle which changes from outside and inside air. I've pulled and cleaned the right most electrical connector which is what I believe actually triggers the ECM to engage the A/C clutch and aux electric fan.
Nothing I've done (and I think I've been quite meticulous) leads me to the issue.
I've checked fuses (moot I think as I can trigger the fan via the relay).

Anyone have any experience with this specific year that might point me in the right direction. The cooling system works correctly and I rarely need the aux fan but definitely need it with the A/C.

Thanks in advance.