‘81 911sc Speedo not working
 

Just opened up my (previously working) speedo to replace an odometer gear. Went fine and reassembled the unit with no visible issues. Have established I have good 12v power and signals from sender unit - yet now the speedometer and odometer don’t work at all.

Anything obvious I could have done to damage it? Suggestions for fix?

Thanks.

I have the same issue. Any ideas? Thanks

Some folks can fix those delicate instruments with a ice pick & a beer can opener. Those folks call me crazy, but everything I've ever done to gauges & instrument has made them worse. I'd recommend a pro. Even most shops send them out to someone with little fingers. The trip odometer gear fix on my '82 cost me $185 @ TRE. Invoice said "sublet." I spent no time on the floor chasing little springs, circlips, & jewelers' screws. Never hurled invective or a wrench. My talents were max'd pushing the speedo back in its' hole.

When I got my '77 gray market 2.7 in 1984 its speedometer didn't work. Transitioning from a VW bus, I really needed a speedometer.

I think I found a burned diode in the speedo. That speedo had two ground spades. If you hooked up only the wrong one of them, some excess current flowed where it shouldn't - something like that. Why both those spades weren't internally connected I never could figure, other than it allowed the speedometer to be used with a positive ground system. Porsche never used that, but didn't Bosch make the speedo?

So both need to go to ground. Maybe by the SCs there is just one ground for the speedo and the instrument lights?

I opened it back up and found 2 wires crimped. Hopefully that was it.

That fixed it. It wasn’t that hard of a fix.