The previous owner install a switch for electric temp gauge to turn off when not in use. Is there a place/spot where I can hookup a wire that will work only when the key is on ?
I don't think an OEM switch would work. An ignition switch that is wired to control power to the coil could certainly be used to operate instruments. Ford started using this set up after they dropped the liquid filled hydrostatic fuel quantity gauges and installed electrical pressure, temperature, and quantity gauges from King Seeley.