Deluxe Audio cassette deck

I just picked a deluxe audio deck out of a 91 GTI and I'm trying to install it in my 90 Jetta Carat. I plugged it into the jetta, and I get the blinking red light, but when I turned it on all I got was a blank lcd. It came with the plugs from the GTI still attached, so I know that the wire that goes to terminal S on the radio was connected in the GTI but not in my car. Does this wire need to be connected to something? Or is the radio just shot (it was sold as working)? I have the code, I just need to get to the point where I can put it in.