Speedometer / Speed Sensor
 

88/911 Having problems with my speedometer. Initially it would not work until after about 5 miles then when the car warmed up it worked fine. Been like that for several months and I’m now get around to troubleshoot it. I’m not sure how to segregate the sensor from the gauge. Pulled gauge and have 12V to it all the time. Brown wire a gauge tests good to ground and there is continuity between the green and brown to the sensor. There is no continuity for either brown or green to ground. Since the sensor is a twisted pair pulse generator I think this tells me there is no problem with the wires. (any advise here?)

I pulled the sensor and cleaned the magnets inside the case. (were very clean). I can put a meter on the green and brown from the sensor and I don’t get anything (AC) when the car is moving.

Any ideas on how to tell if it’s the sensor or speedometer?

Thanks......

The sensor is a reed switch that closes as the magnets go past.

put your meter on ohms and verify it opens and closes.

Rick, Thanks.

Across the sensor it bounces between .2 and .3 ohms regardless of the wheel speed. Have the car up on jack stands.

As you slowly rotate the wheel it should go from open to low resistance. Are you saying it constantly reads < .5 ohms?

Yep, .3 ohms all the time. I rotated the wheel by hand slowly and ran it up in second gear. No change on the meter. I think what you're telling me is the sensor is stuck shut and probably needs replacing?