87 911 carrier speedometer and odometer problem
 

I have a 87 carrera with 21k on it. I drove it last week and everything worked fine. Today I was taking it in for service and on the way there the speedometer and odometer did not work. The shift light is not working either. I had the guys at the shop look at it and they checked the connection to the trans as well as the connection behind the front seats - everything connected correctly.

Any thoughts what the issue is? Every other gauge works fine.

You should start by disconnecting the cable in the smugglers box behind the seats. Jack your car up and rotate the rear tires slowly. Use a meter to check for continuity contacts. Most people say you should receive 8 contacts per revolution.
If you receive no contacts, you will need to replace the sender cable. I had the exact same problem with my 89' and ended up replacing the cable.