Speedo and odometer not working

[BHP231]

Hi all, I’ve just around to getting my 1986 944 Turbo back on the road, I bought it a couple of years ago so I’m not sure if the non-functioning speedo and odometer is a legacy or happened while it was laid up.
The plug on the back of the transmission seems ok and I’ve cleaned it.
I’ve pulled the dash and cluster out and was surprised to find that the gears for the odometer were in good order and turned by hand easily.
So now I’m not sure what to do.
Any ideas are appreciated.

[gb944]

If it is not the speedo sender (on the transaxle), then it is the wiring between the sender and the instrument cluster.

The sender does have a fairly high failure rate.

If you have an oscilloscope, you can hook it up as follows:

brown ground
green/white 12vdc
blue signal to speedo should make a 50 mv square wave when wheel is turned.

[kdjones2000]

You should probably take your cluster to a speedo shop so that it can be tested.

If they have been sitting around for a while, sometimes they work only intermittently. I have had several like that through the years.

[BHP231]

Problem solved…. Cleaned earths, checked diodes, tested the sender on another car and it worked. I swapped the speedometer mechanism behind the speedo face plate with another and it all works now, so a faulty mechanism was the problem.

[gb944]

Originally Posted by BHP231

Problem solved…. Cleaned earths, checked diodes, tested the sender on another car and it worked. I swapped the speedometer mechanism behind the speedo face plate with another and it all works now, so a faulty mechanism was the problem.

Good job diagnosing... thanks for the feedback...

[Deyy6]

Great

[kdjones2000]

I am on my third speedo mechanism now, and it's acting flaky... Good to have spares around, but 160/180 MPH changes make things harder to find.