jumpy speedometer

[canadian booster]

My speedometer from time to time will peg out at 200km/h and then sometimes it'll fall back to normal speed or other times if it stays pegged for a couple minutes the HICAS light comes on. Turning the car off and on again resets it, a 'rolling restart' will sometimes work, but shutting off the car for while will always fix it. Occasionally my temp gauge bounces or jitters

I searched the forums and found someone with a similar problem :

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

I wonder if this maybe is my problem or related to my woes since my 300zx has an aftermarket steeringwheel (with no cruise buttons). The previous owner installed it, maybe they made a boo boo somewhere?

is there a way i can test this stuff before i start replacing parts like speedo sensor, etc?

[canadian booster]

i found this on a different forums, maybe i'll try it first since it seems the easiest solution

i know that the connector for the speed sensor is prone to having oil on it causing high resitance or a short leading to exactly what you are talking about. so first things first. crawl back under there and clean the connector up with electrical contact cleaner or carb/brake cleaner