It seems like people are getting a bit confused, perhaps I can help clarify. To manually trigger the fans, all you have to do is ground Pin 85 on the existing fan relays. I used the ground from the phone connector, you literally run a wire from the ground to the relay. You then interrupt this wire with a switch, so you can turn it on and off. With the switch off, the fans work as they always have, with the switch on Pin 85 on the fan relay is grounded and the fan are manually turned on.
You can do this with a simple switch (pictured above), or the OEM switch and a latching relay. The OEM switches do not stay on or off they send a momentary signal when pushed, so you need a relay that stays on or off when it gets the momentary signal from the OEM switch. I chose to only connect the high speed fans, because the low speed fans come on with the AC, so I didn't see the point. And with the OEM switch, you would need two switches one for the high fans and one for the low fans. If you want both the high and low fans with one switch, you use a 3 position switch, the middle/off position is the ground, then the high and low are the other two positions.
You can also wire the engine compartment fan the same way, by grounding Pin 85, but I haven't done it since the relay is in the rear trunk so you need to route the wire a long way.
I have a write-up on the radiator fan mod using OEM switches in the batwing, and how to get them backlight. It's here:
DIY: Manual Radiator Fan Switch w/ an OEM Switch
Porscha
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