86 5ktc A/C issue

[Montague, Scot]

I changed out the heater core and put a new A/C blower motor in my car. I also had the dash out (and replaced it from my donor 89 200 since a radio thief damaged the 5K dash. Other than some a few modifications and fabricated brackets not so bad a job) I cleaned up the radio wiring that a previous installer hacked up and moved the diff lock to where the ash tray was on the 200. As relatively painless as all that was, I'm vexed by the inoperative A/C head unit.

My question is where do I look to track down the problem with the A/C? Before the heater core replacement the A/C worked fine, head unit and controller worked fine, now the head unit  gets power to the side illumination when the headlight switch is on, but the LED and the buttons are dead. Nothing powers up. Before the heater core removal, everything worked. Any ideas of what I might have left disconnected?
I checked fuses, the head unit has the wiring harness plugged back in, (I swapped out with another head unit and the symptoms are the same) and  I looked at SJM Autotechnic's fine A/C section. I'm just about to remove the center console again and examine all the connections,  but I want to see if an easy answer is available.

Scot Montague

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