So I wanted to wire up a switch that could manually turn both fans on whenever I want and still have the stock fan system work. I thought that splicing a wire into the green/white wire coming out of the fan relay and connecting it to ground with a switch in between would work, so I did this and found that it only turns on one fan. Then I realized there were two fan relays - so I spliced the ground wire on the other relay(don't remember the color) into my existing wire, so basically both fan relay ground wires are connected to each other, and are connected to ground whenever I flip the toggle switch. This setup seems to work normally with just the key on and the engine not running, but when I turn the engine on, both fans come on and stay running the whole time, regardless of the switch. As a test, I cut the wire running from the switch to the fan wires, so just the two fan relay ground wires are connected together, and the same thing happens - they both run all the time with the engine on. Why is this? Is the only option to run two toggle switches, each one separately grounding the wires to the fans? This doesn't seem to make sense - could anybody shed some light on this for me? Thanks!

P.S. Sorry for the long post

 

I was thinking of doing the same thing. I did a search and found this question.

The most likely reason the fans came on is because there are many ways for the relays to get a ground (not just your toggle switch). I bet the engine was warm and the fan switch was providing the ground. The gray wire is the one that connects to the fan switch.

Does anyone know of a way to 'splice' into the relays without cutting the insulation on the wires? Is there a way to maybe 'back probe' the relay and get a good connection?

It would be cool if a device existed that would plug in between the wire connection and the relay that you could tap into.

Does anyone know of a reason why you shouldn't splice the green/white stripe wire on one relay and the gray wire of the other relay so that when the fan switch (mine is an on at 200 degrees) cuts on (grounds), both fans will come on?