I am the proud owner of a 1993 full size chevy blazer 350V8, 4x4, auto My problem is the speedometer is jumping even in park i am doing 70+ MPH. I was told the VSS was the problem but the wrecking yard told me the cluster was the problem and i replaced it with the same results. Also the ABS light has been on for over a year.
Possible solutions
1) ECM ground wire?
2) VSS
3) ???
i had this problem 5 years ago and it corrected itself
also it happened after i jumped a Ford

 

I would definitely suspect the VSS before the gauge cluster.

 

I took off the wire to to the VSS sensor and it still had the problem. I have replaced the cluster to no avail. After having a transmission shop put it on the computer he told me the ECU must be bad, Guess what i just bought a new ECU and i still have the problem.
Lets check the score card
1) cluster $75
2) shop service call $80
3) new ECU $119
Knowing never to jump start a Ford Priceless

 

ECU... Well, I would have suspected the DRAC (Digital Ratio Adapter Controller) module before the ECU as well. It is also possible that you have a wire grounding out somewhere under the truck or under the dash.

 

do you have a aftermarket cd player....One time a guy in the town i live in put one in and his speedometer was jumping like that...it finally burnt his alternator up some how.. it does that every time he puts a cd player in it.. its the second time its happened.