chrisgilbo

I am at a complete loss for what I can do next. My speedometer has been acting up on and off for the last year or so but just in the last few weeks it has completely gone haywire. I am having to use my GPS to track mileage for fuel and MPH. My first find was to exchange the speedometer (instrument cluster) with a known good one and doing that only lead to the same results. I have checked grounds, checked fuses, cleaned the terminals on my battery, checked the voltage while the truck is running (13.86 to 14.06) to make sure the alternator was putting out the correct voltage. I just don't know what to do next or what else could be wrong the be causing my speedometer to do what it is doing. Please see the below YouTube link to see what it is doing for yourself. PLEASE HELP!!!! I am losing my mind. Thank you.

mulmur1

Welcome to the forum.

I think you are on the right track with the grounds. Did you take the grounds off the truck on the driver's side frame rail and sand off the contacts? I assume that you didn't use any anti seize on the grounds, as this will block a good ground. I would trace all ground straps, hood to firewall, frame rails, engine block etc.

Unfortunately, I have seen this on one of my trucks and it was a ground problem. I also had the stepper motor problem with the instrument cluster, but you have confirmed that your cluster is good.

Good luck with the repair.

chrisgilbo

Thank you for your reply. I have traced and cleaned the battery ground on the battery and the two grounds bolted to the studs on the firewall in the front of the drivers side. I know there are several grounds. Can you tell me where else I should look. where is the ground located on the engine block? Thank you for your help.

mulmur1

Chris,

There should be two additional grounds under the driver's side front door. They are located along the frame rail. This is really prone to rust and may be the area where you are getting the poor ground for the instrument cluster. There should be another ground cable from the engine block on the driver's side on the engine to the fire wall. It is normally located near the back of the engine and may be hidden under a cover.

I would look at the frame rail first and I believe that may be the problem. Good luck with repair. Hopefully this will fix it for you.

in2pro

I would also check to see how it works with the IP pulled out and connected, make sure nothing is pulling/pushing on the connectors on the back of the IP, also check for any cuts or shorts to the harness....
Do you have any aftermarket accessories? if so check that they are properly installed and grounded...

I'd also check under the hood to make sure noting is shorting to the engine block, and that no wires or harnesses are draped over or near any of the spark coils, wires or plugs... I had a similar problem on a 1993 truck that the tach and speedo would act up, turned out to be a bad plug wire arcing....

chrisgilbo

So I checked the ground on the drivers side door, cleaned it and then checked the ground under the truck attached to the engine block and cleaned it but I still have the same results. I do have an aftermarket radio but the connections in it are good. The only ground i cant get to is the braded line connected to the firewall. My buddy made the suggestion that it might be the BCM. Is that possible?

chrisgilbo

Okay so here's another strange one to throw in the loop. To start off with when I got in my truck this afternoon and turned the ignition all was dead on the speedometer except the engine light. After checking all my grounds and connections I decided to check and see if the truck had any error codes stored. I have a USB diagnostic reader the igs into my laptop and I noticed as soon as I plugged it in the speedometer lite back up and started working. (Just a side note the cluster works with it plugged into the laptop and not) I then drove my truck down the road and everything worked fine even the cruise control. But the second I unplug it my cluster goes out. I am just so confused.

chrisgilbo

Does anyone have any idea of what might be going on with my instrument cluster?

hfdff

Not sure if you fixed your problem yet. I know your said that you checked your terminals but here's a website thats pretty good that you might want to check out.
Sparky's Answers: 1999 Chevrolet Suburban, Erratic Speedometer Caused by Burnt Battery Terminal

chrisgilbo

Thank you for the suggestion but my terminals are fine and clean and still the issue continues.