Speedometer doesn't work, but odometer works

[bose213]

Hi.
The Speedo on my 911sc 1979 doesn't work. However, the odometer works great. I checked the wiring, and it's correct. The sensor is working and reading all magnets in the transmission.

What could be a problem?
31b connector is giving 5volts, is it okay?

Thanks.

[Matthew_VA]

refereshing this thread. working on another project but I measured 5.2V off the 31b terminal.

For the community, a question I have is, so the speedo measures the speed through a ground pulse with every magnetic pass (basically a square wave) and the faster the "pulses" occur the faster the speed is shown on the speedo, right?

[jrwilson]

There's probably a loose connection inside - a cold solder joint. If you open it up and run a soldering iron over each point to refresh it, it might start working again.