Trinary switch and fan wiring

Mitch Krause

Silver Supporter

I did a bunch of web research, looked at some images and readings on forums here, and tested as much of the circuit as I can. I think I have the wiring for the electric fan and trinary switch figured out and hopefully correct. I am intending to wire in a manual switch so that I can have a separate independent control to turn the fan on. I am hoping that someone that is more familiar with the circuits than me can look at the diagram in the picture and confirm that I have things right. I have the older style hot rod air setup.

I also have the current fan temperature switch at the bottom of the picture and have a specific question about that. Specifically, it has the single blade on it for connection, if that type is used (it would be threaded in the pipe at the front of the car where the hot water from the engine runs), will I have a problem with this type? My concern is that when it activates, it would not have a good ground being in the pipe that doesn’t have a specific ground. Or would the fact that it is in the water let a good enough ground connection be carried through the water?



Hi Mitch,

Attached is the final wiring I use on my A/c system. It took a long time to resolve, mainly trying to understand how to wire in the trinary switch

I agree with previous posters that the switch shown needs to be grounded to function, but are you sure it’s not a thermal switch, not a temp sender. If it’s a thermal switch, they normally have the switching temp marked on them

On your wiring diagram, you need to check the main switch, as drawn it will ground the 12V supply. Switch should be on the 12V feed to pin 85 on the relay



Mitch Krause

Silver Supporter
Andy and all,

Thanks. It did finally resonate with me that the relay needed to be a ground activated one with the polarity reversed (if that is the right description). Then the fan temp switch, the manual switch and the trinary switch all have the capability to turn the fan on by switching to ground. So I think I have all of that figured out now. Final wiring diagram attached.