That headliner issue is exactly what happened with my carWent live today with the battery, no smoke and no fires. Was a little nervous after lots of wiring work over 2 years. No engine fault codes either.
Only issues i noted so far is that somehow all of the central conv. coding reverted back to factory, the brake switch turns off the lights instead of turning them on (not sure if coding or wiring since i went with a MK4 switch), the coolant level sensor is beeping even though i wired it so it should be off, and even though my headliner was in perfect condition when i parked the car i noticed today that the entire center section has separated. Only noticed it when the wife went to put the battery cables on and hit it with her head.
Next week I’ll swap in the built trans, wrap the rest of the engine harness and start installing the rest of the drivetrain.
Fill all fluids
Double check all engine hardware torque
Loom rear section of engine harness
Bolt up axles
Route PCV hoses/figure out catch can solution
Put new fuel in tank
After that it’s driving. Not sure if the 70A alternator is enough, but we’ll find out
My Golf, Passat and now GTI all have saggy headliners
That headliner issue is exactly what happened with my car