Speedo problem has me confused

[AK Rover]

my speedometer and odometer stopped working a while ago and I'm running out of ideas to fix it. I've replaced the instrument cluster as well as the rear wheel speed sensor. I have also checked all fuses listed as relating to the instrument cluster. None of this has fixed the problem. When I enter test mode all gauges, including the speedometer, sweep normally.

What really has me confused is why the speedometer goes up to 40mph when I turn the dimmer down while the headlights are on then it goes back to 0mph when the dimmer is turned back up. Has anyone else experienced this?

I've searched this forum as well as others for an answer and can't find anything. My forum searches is what led me to believe that the rear wheel speed sensor could be the problem.

 

[AK Rover]

After some thought I decided to investigate and see if I could figure out why the dimmer switch was causing the speedometer to react. I realized the problem started after re-installing my aftermarket stereo so I decided to start there. When I pulled the stereo out of the dash I found that the shielding on a few unused wires had pulled off and the exposed wires were touching. I clipped all the unused wires on the wiring adapter so that there was no exposed wires to touch and cross feed. In the process I drained the batteries because they were weak from sitting overnight in negative temps so I haven't been able to go for a drive and see if the speedo works but it didn't seem to be responding when I moved the dimmer anymore. I'll report when I can if that was the problem.

 

[AK Rover]

Problem is fixed. Wires behind the stereo were shorting and causing the speedo problems.

 

[DaveBen]

Glad you got it fixed.

Dave