Nissan Repair: Spedometer, nissan 300zx, transmission shop

Question
I have a 1987 nissan 300zx with a digital spedometer. it went out but not completey. it reads 0 but is on. When that went out the overdrive went out. I took it to a transmission shop and failed to get it fixed because the sensors in the tranny work. im guess the control module for the spedometer is bad. where is that in the car and how would if fix it. i found out from the transmission place the reason the overdrive isnt working is because its connected to the spedometer and that on and off when it reads the right speed and now that it doenst read a speed means its not activating. so if you have any suggestions i would appreciate it.  

Answer
please go to this link http://www.phatg20.net/modules.php?name=Downloads&d_op=getit&lid=239 and if that doesnt work go here http://www.phatg20.net/modules.php?name=Downloads&d_op=viewdownload&cid=67 and click on 86 or 88 and download the factory service manual, and search through this to find your answer.  it will show you a far better description than i can put into words.  good luck and let me know if this helps you! xxp_sebby@yahoo.com