My books are for a '94 and it doesn't show a green wire in the diagram. I'm no Cadillac expert, and I could speculate about how you could wire it but I don't want to sound like a dumb *ss if I tell you the wrong thing. Electrical diagrams aren't a great strength of mine but I'll try.
If it's similar to my '94, from what I'm interpreting, the motor contains 2 striker switches and a lid open/lid closed switch internally. The motor gets constant power and a constant ground. The striker switches are hot and the lid switches are grounded. They work in a "domino effect" way. Switch 1 gets the signal from the trunk release and tells switch 2 to trigger the motor, the lid ajar or lid closed tells the motor which direction to go.
In this case I think your green wire is your trunk release, red is your constant hot, and the two black wires are grounds.
Now....if you already have a trunk light in the car, it should have a grounded contact that controls the light on and off when it opens. All you would have to do is figure out which, if not both grounds changes the direction of the motor to close or open the trunk and make it coincide.
Hope this helps somewhat. Like I said, my car is a different year and I might be telling you the wrong thing. If the resident Caddy expert wants to chime in feel free :wink: