91 PA speedometer crazy

Hi guys. My son is driving my old 91 PA. His speedometer is going crazy. It will show various speeds when driving or even sitting still. I have replaced the VSS and the ECM and still have the problem. What am I missing? Could it be the Speedometer itself? Is there a module on the back of it? I'm at a loss here.

I would say the dash is the problem. Had simular problem on my 92 and it was the dash, I believe others in this forum have had the same problem. After replacing the dash the problem went away.

Let me just point out, you must make sure the car you are getting the dash from has the same options as yours. Not every dash is the same in the same year car. Low fuel, alt. led light, are some options that run through the dash. The first dash I bought I could not use cause it did'nt have the low fuel and alt. led option. It still worked but I was without the options. Plus I think its important to match it perfectly, same amount of wires at the hook-up and all. The second one worked. Some of the gauges have two prongs, some have three. This is important as well. The prongs you will see on the back of the dash. If yours is a 3 prong and the dash you bought is a 2 prong, that gauge won't work. Just study the computer boards on the back of the new/used dash if you go that route. Any more questions just ask! Good luck!