I replaced the single wire sensor as suggested in another thread on this site, but the temp gage still climbs from cold to hot when I turn the key to on position, or when it's running. I just got the car a few days ago, and have been fixing it up. Put in a new radiator, termostate, and temp sensor yesterday.
Any suggestion on why the temp gage continues to act up, and possible fix to solve this problem?

It also has a tachometer that goes backwards that I need to find a solution to. I don't think the 2 issues are related, but thought I'd give ever detail I could.
Could I have a gounding problem that is effecting the temp gage, and where would I look to find it?

 

It's a automatic tranny if that makes a difference

 

Disconnect the single wire to the temp sensor and turn keyswitch to ON. It should stay at Cold position. If gauge rises to Hot, there is a short in the wiring or gauge panel causing the problem. Note, manual says a continuous short of the wire may damage the gauge panel movement.

If gauge stays cold, turn keyswitch to OFF, short sensor connector wire to ground, and turn keyswitch to On. Gauge should begin to rise towards Hot. Stop the rise by turning keyswitch back to OFF.

good luck