No analog dash gauges and climate control. Not the usual suspects…

Could use some advice re this one—thinking it could be the Time Control Unit?

Car is a 1987 GL MT no factory cruise control. Analog dash gauges and climate control.

So, like many others, I've lost my dash cluster/climate control lights after a stereo install. When installing the stereo, I had to do heavy repairs on the factory radio harness due to a prior install. I've since replaced it entirely with a good uncut factory harness with same part numbers. I also used a floating ground adapter and a receiver wiring harness (typical Crutchfield stuff) to keep all factory wiring intact.

Things that I've checked/replaced:
- All external lighting operational.
- Brake lights and all indicators work.
- All interior lights work (other than dash and climate).
- Cigarette lighter works.
- Windshield wipers/delay works.
- I've removed my rear wiper—so haven't checked that, but have it on-hand.
- Replaced headlight stalk/switch with new Japan-made unit from RockAuto (looks exactly like factory in every way).
- Dimmer switch is getting power, so could be bad switch.
- Tested another dimmer switch from a GLL with pigtails. No joy. Could also be bad switch?
- Checked/tested all fuses with light+multimeter.
- Checked fusible links under the hood by battery. No burnt wires or any weirdness.

I'm wondering if I've shorted something out. Where else is there to check?

I'm also wondering if the Time Control Unit could be damaged. How possible is it to damage just the illumination functionality of the unit, while everything else appears to be operational?