Nissan: Locating the speed detection circuit lead, 1990 nissan 300zx, nissan 300zx

Question
Hi, I have a 1990 Nissan 300zx 2+2 (non Turbo). I recently bought a navigation system from Pioneer, the Avic-N3. I self installed everything, however, I have one problem. I need to connect a wire from the navigation hide away unt to the car's speed detection circuit lead. This will allow the navigation to detect the distance the car travels. The navigation instructor's manual says that the speed detection circuit lead is a wire comming off of the vehicle injection computer. I can't find this computer or wire. Even if I do find this computer I wouldn't know what color this speed detection wire is. If you have any idea of what this is and where to find it, please contact me. I took apart half the dash looking for it. Thanks a lot.

Answer
The ECM is under the passenger floor area. You will need to get a schematic of the ECM and find the wire from the speed sensor that comes out of the trans. Give me you VIN#, production date and your e-mail if you cant find a schematic and I will send you one.