Blinking LO 4wd light + others

2007 SR5, 5.7l, 4WD
all this “fun” started after a A/C expansion valve replacement, which requires removing the entire dash and support framework.
Getting P712 (I think that’s the #) - no signal from vehicle speed sensor.
Didn’t touch any of those wires.
Tested sensor - ohm’s out to spec.
Dealer ran tests, truck shows it’s in motion when it’s sitting still - they suggested ECU was toast.
Sent ECU to SIA - they tested it and report no issues.
Pulled dash out again and double/triple checked that all connectors on both harness attached to dash and harness attached to dash frame were properly mated and no extra connectors were homeless. Same result.

Also - no backlight on A/C or radio, and when you turn the headlights on, the info center and radio display turn off (radio still plays) instead of dimming.

Seems to me kinda like we’ve got a ground wire hanging loose somewhere, but I can’t find any.

AllData says there should be a ground in the following places:
Driver’s door jamb - found it
Steering column - not found
Left side of dash support frame - found it
Right side of dash support frame - not found
Under passenger seat - found it
Passenger door jamb - found it.

Any ideas?