Dc motor control with optical encoder (head light adjuster)

Hey guys, I have a ford fiesta headlight adjuster it has a small dc motor which has 13v written on the side, its part of a pcb with an encoder. Thought it would be great to get working as it has a circuit already completed. Ford technical guys say that it’s controlled straight the the switch on the dash board which has a potentiometer inside, so thought this would be easy to just plug in and go using the pwm. But doesn’t seem that way!

Attach a few pics that help show the idea, any help or thoughts would be great.

Regards Richard