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The reason I am gonna use this setup is for hands free automation. 1st stage on the VW switch activates the low speed on the fan, 2nd stage activates the high speed. This particular switch was designed to run TWO fans though, so when high kicks in, low is till active. This would detroy the fan motor if wired with traditional relays. That where the Volvo relay comes in. When low I triggered, it turns the fan on low peed. When high is truggered, even though low I still active at the VW switch, it SWITCHES inside the Volvo relay to high side only, effective acting as a 2 speed controller. This means that I don't have to manually hit a switch to toggle high or low on the fan, giving me a cooling fan sytem that operates like it would in factory designed system



The Volvo "box" is just two standard relays inside that are wired in such way that when hi is active, low is deactive. That is easily accomplished with two standard relays and wiring them together so they perform the same task.

With the VW switch, you'll have to make sure if thermal contact 1 is activated (say at 180) and then thermal contact 2 is activated (say at 220), it doesn't unground contact 1, or it won't work with the Volvo relay block. You can still use the volvo block for hands-free operation of both speeds, and just install two thermal sensors in the engine.