Replaced Heater Core now no start

Replace heater core, had battery unhooked for the duration. Reassbled and now car will run and die after 2 seconds and my immobilizer is flashing. My bad, used valet key off the hop to try to start the car. Can not connect to general obd will not read but got codes through VAG com. Immobilizer pick coil, key signal too low, ECM no communication. Abs and air bag. I’ve checked all fuses seem to be good, tried all the tricks on you tube. Also not getting my glow plug light either when key is turned. I have had the cluster out and checked the connections. After first assembly the gauge cluster was blank. Took it out and redid the connections now it seems to be working. Help!

Check all the connections to everything on the steering column, too, as well as all the ground points.

There are 2 grounds at the air bag connection would that do it ? Steering wheel is currently removed

Among the tricks on youtube, was one of them putting in the proper key
and turning to ON position and leaving it for 15 minutes?
Also, is your 109 relay black (old/defective) if so replace with the new gray model.
But try the key thing first.

I bet it’s missing earth points like oilhammer and trgreen says