will auto temp guage work on outboard

[kingfisher2]

i purchased an automotive temperature guage and thermostat.i hooked it up where there was a plug right beside thermostat.dont get a reading from guage.if i heat up outside block guage works.will this not work or is water too cold beside thermostat to get a reading.oh ya motor is a 1989 70 hp 2 stroke.
the only spot i see to mount sensor on cylinder head is where the thermo switch is located. could i tap into pink wire with my temp switch wire for my temp guage.

[boats.net]

The temp sensor needs to be mounted on cylinder head.