z31.com | Message board: A/T to Manual Swap Instructions
Try this link and then go towards the end of the document where it talks about the transmission wiring.
The problem is the inhibitor switch that is now missing since you have a manual. What I did is wire the inhibitor switch to a switch I put in the spcae for it in the console next to the mirror switches. The switch I used was a turbo headlight washer switch. YOu press the switch when starting the car and once started release it. This way the cruise control will work and you also have an additional theft deterent as the car will not start without the switch depressed. I did the tranny swap in December.