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.

[Longhorn Man]

Welcome to the board!
The passenger side sensor is for an early smog device that hurts MPG and performance. (I can never remember the name of it though) 99% of them are disconnected and thrown away.
It hooks to a switch in the tranny that senses when it is in top gear, the sensor in the head that tells it when the engine is up to full temperature, and only then will it let the vac advance in the distributor come on.

[gclark]

Longhorn Man: Thanks for the reply.

That would make sense. I do remember seeing a wire to the transmission that I could not identify.

[ERASER5]

LMH is right. The system was called the Transmission Spark Control. There was a relay, a transmission switch, a vacuum switch, and a temperature switch in the passenger head. The switch closes at 32 degrees and above, so it only opened in the winter. I tested mine before giving it to a fellow board member. Just remove the vacuum switch going to the dizzy vacuum advance canister and any and all of the other parts connected become optional. I used the key-on hot wire for my electric choke.