Both have stopped working, i talked to a person over there phone they said i need to check my sending unit.. I have no idea where that is, could anyone tell me?
Thanks

While not being familiar with your make or model as well as the Bonneville. There is typically a speed sensor located on the case.

Took my truck to a mechanic he found out that the people who installed my after market stereo clipped into the cruise control/speedsenor wire for a hot so it shorted the power to the speedometer and odometer. The mechanic rewired the stereo and everything works just fine.