My speedometer is stuck at 160ish mph.. I bought an instrument cluster on Ebay but it does not work!!! even though the instrument cluster i bought has 10k more miles, I dont care because I need to know how fast i am going at ALL TIMES!! Mazda dealership quoted me $1400... I would like to know IF THERE IS SOMEONE OUT THERE THAT KNOWS HOW TO BYPASS SOMETHING TO MAKE IT WORK... PLEASE HELP ME..

 

Not sure how to fix this. Meanwhile, while you explore how to fix this issue, I would recommend to install a GPS App on your smartphone (Android or iPhone) and do a dash or vent mount of the phone to check your speed via the App.

 

You may have a short in the speed sensor circuit somewhere.

 

The cheap way:
- Use a Garmin, your phone, or a Scan gauge plugged into the diagnostic port to read the speed. Or,
- Stay with the flow of traffic. Or,
- Figure out steady speed RPM vs speed. For example, have a friend match your speed in another car. Using hands free cell phone, your buddy can tell you how fast you are going while you take note of the tachometer reading.
All the above are way less than $1400 unless you have to pass a state inspection.

Did the Mazda dealership specifically diagnose the problem as being just the speedometer? If you trust the diagnosis, see what an independent shop can do.
There are also some businesses that specialize in gauge cluster repair...look online.

If a scan gauge plugged into the diagnostic port displays a proper speed, then you know the speed sensor and computers are ok.

Did the Ebay gauges have the same or different problem? Same speedometer problem suggests the root cause is not the gauges.

 

The days of replacing instrument clusters is long gone. They are part of an integrated system including the ECM/Ignition switch/Key fob/Immobilizer, etc. etc. Likely the only way to get things going again is to plug the car into the big computer at the dealership for reset.