Mine came not plugged in from the factory but it looks like you already checked that.

There's also a 2 pin connector for the stewie motor in the playfield wiring harness under the backbox that can cause issues.

It unplugs itself easily during movement or working on the playfield. Just make sure the molex is tightly plugged together.

Having same issue with mine. I am pretty sure that I am getting power to board but nothing from motor. Anyone know where to purchase a motor?

Just had this issue and sanctumwear was spot on.
There's a large 2 pin connector with a black and a red wire that was unplugged. It's right where the playfield harness comes out of the convoluted tubing from the backbox and plugs into the main power wiring harness.
Hope that elaboration helps. Looks like pulling the playfield in and out would easily disconnect those if hung up AT ALL.