Your tilt motor has 3 electrical points.
12v+ blue = Up (sky)
12v+ green = down (grass)
12v Negative - gets this from mounting points. Why yours has a separate ground wire for the chassis might have to do with the gasket between tilt motor and Intermediate housing. I don't have that issue with mine. When you want drive up the blue wire gets power and green does nothing. When you want the drive down the green gets power and the blue does nothing.
There is also a overload inside the motor that kicks out if it sees a "locked rotor" (motor not spinning) and current spikes. I had to clean my contacts up but this is not meant to serviced. There is a little plastic thrust washer next to the hammer blow coupling that if missing will cause things to bind. I had to completely disassemble the whole motor/gear assembly to get to work right