I have a '92 940 turbo w/a vexing speedo problem too. My speedo differs from yours by only the turbo boost gauge. This speedo stays on zero unless the ambient temp is cold (<50), then it will work for a few minutes before falling back to zero. Sometimes it will jump up to 45mph and stay there. The odometer is inoperate as is the cruise control.

My efforts so far are:

swapped the entire instrument cluster for another which I got at a reasonable price on ebay. No change, the replacement cluster acts exactly as the original did.

replace the sending unit from the differential, no change. BTW that little sensor is very pricey and I'm sure my old one is good. If yours is out of value I'll let you have mine very cheap.

I've traced the wires from the back as far forward as I could and found no breaks.

The FAQ on the 740/940 models suggested perhaps the ground for the speedo cluster is the culprit but I'm not sure where that is.

I'm eager to know when you find a solution to your speedo problem


cogito ergo zoom,

passport