So, I decided to dive in and turn the shaker motor on as suggested by others here. Here's the problem - it doesn't work.

I have taken the motor board out, tested all three fuses for continuity off the board - all 3 are good and all 3 are 2.5A each. I tested each diode; they all read 0.477 - 6.00 so those are good.

I cleaned all the male spades that all three female end wiring harness connect to the motor board; they have no corrosion on them, and all three wiring harnesses that hook up to thise board have been unplugged and re-seated.

So, what's next? Where do I go from here? How can I test the motor to see that it itself is good? Do I need a 12v source to power-test it ?

Fixed it - it was a bolt that was crooked in the shaker motor holder keeping it from moving correctly. That and the pendellums on each side were right up against the mounting brackets - keeping the motor from being able to move.

I didn't have to go that far. The shaker connects onto a a PCB board directly above the motor.