I replaced the sensor on my 86 n/a. It lasted for a day then went back to not showing speed again after a short drive. What could my issue be. Other than a loose connection?

 

Sorry, it's a digital dash

 

Make sure all the connectors are clean and free of any corrosion, if the sensor is new, then most likely it is a bad connection somewhere. Take a look at the FSM wiring diagram, make sure your grounds are good, as mentioned before, not a bad idea to make sure your battery has a solid ground to the frame, and an extra ground wire can be run from the frame to the intake plenum. You can download an FSM at XenonZ31 Reference

 

No reading?
Reading zero?
Jumping around?

 

busted speedo cable or jumped out of the socket on the tranny.

 

Just figured it out. When I replaced the power supply for the dash. I dropped the nut that attaches to the frame down in the carpet. I figured it was ok to just screw the one back in on top instead of fishing out the nut. DEAD WRONG. The nut is actually part of the ground which would make it work some of the time. Fixed one problem and created another. Lesson Learned.