1972 passenger side temperature switch

[gclark]

I have a 1972 C10 with a 350. I want to add a temperature gauge but am having a hard time finding a place to install the sensor. I would like to keep the idiot light which is wired to the temperature switch in the drivers side cyl head.

There is also a temperature switch in the passenger side cylinder head. I can't figure what it is for and am considering replacing it with a sensor.

Both switches have a wire going to them. Drivers side= dark green. Passenger side= dark green/white.

I was able to make the idiot light come on by grounding the drivers side wire, but grounding the passenger side wire did not make the light come on.

Does anyone know what the temperature switch on the passenger side might be for?

Thanks in advance for any help.