Hello all! Brand new to the forums, any help would be greatly appreciated.I have a 1991 300zx NA that I have been restoring with the help of my 14 year old daughter, it is going to be her first car. All has been going well so far, but there is one issue that we are having. The speedo is pegged past 160 and does not move. I took the instrument cluster apart and manually moved the needle back to zero. I plugged it all back up and started the car and all seemed fine. Took the car for a test drive and as soon as we started moving forward the speedo pegged back to where it was past 160 and is stuck there again. I can move the needle freely by hand, but it does not return to "zero" on it's own. I was thinking it may be the VSS but the fact that the needle doesnt return to zero on its own makes me think that it may not be the VSS. Any ideas? Anyone else had this problem and fixed it?Thanks!

Moving the needle by hand isn't good to do. Take the car out and test if the cruise control works, if it does then chances are that you just need a new speedo gauge which can be had cheap, this is what I had to do to mine when I got the car and the speedo didn't work. If cruise control doesnt work it's likely that your speed sensor is bad and needs to be replaced.

I conducted the test you suggested, and the cruise will not engage. I never thought of that. I ordered a speed sensor just a few minutes ago. Thanks for the great info!!

No problem let us know if it fixes the issue or not. There is a possibility that moving the needles could have messed something up on the gauge itself still.

This really getting frustrating, I replaced the speed sensor and it did not solve the issue. I got another gauge cluster from a salvage yard, did not solve the issue. I am just at a loss? I traced all the wiring from the speed sensor to the gauge cluster, everything seems to be in order there. Any one have any ideas?

Ok, so I was at wits end over this deal. I replaced the VSS, and the gauge cluster with no change. I found the wiring diagram online that showed that the wires from the VSS are also tied to the ASCD (automatic speed control device for the cruise control) I wondered if maybe the ASCD was bad and was somehow backfeeding voltage or breaking the circuit somehow. I unplugged the ASCD (it is in the passenger floorboard under the ECU) and voila, the speedometer and tripmeter started working. So, I will get the ASCD from salvage car I got the gauge cluster from it all should be well!!!