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.
See you down the ROW
1994 Accord EX
2003 Acura MDX
2006 Acura TSX