Hey guys I've got an issue with my speedometer since I bought it but now has gotten much worse. I have a 99 blazer 2wd 4 door and the speedometer will bounce around and go down to zero while driving if I hit the panel underneath the steering wheel it usually will go back to working for a few minutes. Cruise control does still work when speedo goes out and transmission will still shift just fine and I stronglyrics believe it's a grounding problem. Things I've tried to do to fix it are:

1. Swapped another cluster in (same issue still)

2.took the panels off and looked for a ground that was disconnected or broken(never found one)

3.checked wiring from transmission for damaged wires (didn't find any)

Is there a ground hidden somewhere I missed any help would be appreciated. I've included a video link to show what its doing.

You can hear at the end where I hit it and it started working

Thanks for looking

 

Anybody?

 

Check the passenger side of the overdrive housing, at the rear of the transmission for your speed sensor. Sounds like it is bad.

 

Thanks for the reply. I actually tried it earlier today problem is still there. I did notice that if I gently tap to the right of the radio it will make the speedometer bounce or will make it work again until I hit a bump or it just stops, I have an aftermarket radio if that helps point to anything.

 

To me that points at the radio. Since that's the area your "technical tap" works best. Check the radio wiring.

 

I couldn't find the wire color for your 99. Your factory radio had "SCV" speed compensated volume. It increased radio volume as the truck sped up. Most aftermarket radios don't have that feature. If that wire was left dangling because it doesn't do anything, it could be touching something and interfering with your speedometer.

 

I pulled the radio out this morning and traced the wires back like you guys said and I found that scv wire you were talking about it looks like they cut it in two parts for some reason the piece furthest back they left it exposed and it was grounding out so I touched it to ground and the speedometer went crazy so I cut it off capped it wrapped in electrical tape and so far so good. Turns out I was looking in the wrong area the whole time, thank you guys for all your help, and Happy Father's Day everyone

 

Mine had similar problems but mine is a 4wd it was a wire that run over transmission which had two female ends that tied the speed sensors together come loose