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2010-2012 Range Rover Sport
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Hey guys, I will post a full write up later (with pics, diagrams, etc) as to why I'm doing this. We can discuss pro's/con's later in that thread.

For the moment, I need a bit of wiring help.

I'm using 3 relays to drive a 16" Spal electric fan (with my own custom shroud):

1. Low speed relay (triggered by a BMW dual-temp thermostatic fan switch)
2. High speed relay (ditto . . .)
3. A/C relay (ideally triggered when A/C is requested, basically an A/C request will activate relay 3 to then ground relay 2 and therefore give me high speed when A/C is requested)

I use this exact setup on my 02' BMW M5 and it works terrific. (this is a super common modification in the BMW world when using aftermarket fans or radiators)

My plan was to use the existing viscous fan connector wires to drive the relays. The existing connector has 5 pins. I'm getting 12 volts at key-on with 2 of the pins, so that takes care of my voltage for #1 and #2 above.

I knew before I started the project that the ECM uses a pulse width modulated signal to drive the fan so that it can vary the speed appropriately. I can see this voltage variance on 2 of the pins so I can't use those.

There is one pin where I'm yet to get any voltage whatsoever. I had assumed (it appears wrongly) that perhaps that pin would give me 12 volts when the A/C was turned on (this is how many cars are wired). However, I just tested this and even with the A/C on I still don't get voltage on that pin. I did verify with GAP IID that the compressor is being signaled "ON". Obviously the pin is there for a reason but I'm not sure what.

So, long story short, does anyone know where I can pull a 12 volt signal as the A/C is turned on? I'm sure there is a wire coming out of the ECM I could use but I would prefer not to do it that way (though I will certainly use that as a last resort if need be). I can probably tap one of the wires going into the compressor itself but it's a bit inaccessible on these vehicles.

And yes, I have looked in the wiring diagrams for my vehicle. While I'm very much mechanically inclined, wiring diagrams are Greek to me for some reason. If someone is good at reading these things, and they are bored, feel free to take a gander at the wiring manual here:


That's for a 2005-2009 vehicle but I'm assuming the wiring for the fan is the same. (it does mention a viscous fan in the document but I don't see an exact pinout for the 5 pins)
 
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