Testing an Audi lift gate motor?

This is a motor for lifting the tailgate of a 2008 Audi Q7. The rear lift gate is heavy- there are 2 motors. 
 

The motors stopped working. Prior to their demise, the tailgate seemed to struggle intermittently. The electronics still unlock the door, and both fuses are good. 
 

I'm thinking it's possible 1 motor died, then for 6 months the other one struggles along trying to do double the work, and eventually died too. 
 

The other possibility is that the switch operates a relay or had circuitry to control both motors, and that component is dead (and the motors still work). 
 

The other possibility is that I'm an idiot, and there is something else wrong. 
 

Id like to put 12v on these motors and see if the motors are functioning before I just start ordering motors and parts. But I don't have a wiring diagram. 
 

Any thoughts on the best way to test or troubleshoot this?

Given their larger size, it would seem that #9 & #10 are positive and negative...but which?  

With a trouble light to the harness side see what happens to the light when you hit the switch and are in slot #9 & #10 (or #10 & #9)

With + and - figured then with some lead wire attached to your battery cables touch #9 & #10 to give them some juice.  Any action?  

Any chance you can see what color wire correspond to 9/10?

I would guess getting them wrong doesn't matter, one way it will retract, the other extend. Like window motors. 

There are many on ebay.

In reply to John Welsh :

Yeah, I was aware of the eBay posts (and their wide range of prices)

Your above post seems like a reasonable method. Gonna be a few days before I can test it.