Manual Cooling Fan Switches

[rick3000]

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

[jaykay]

Originally Posted by rick3000

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

Yes this makes perfect sense and I am not sure why one would need more than one relay to ground three pin 85s for all three fans to come at once via a stock momentary contact switch. Three leads through s latching relay to ground. One switch in the empty spot up top controlling it all.

Not sure why one would want low fan speed as well as hi.....it's the same fan no?

I am curious about what the seat heater switch does. Can the two different positions trigger rad fan and engine compartment fan separately .....with two relays of course ( not sure how a step works)

[Dannxx]

Originally Posted by rick3000

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

Hi Rick I am new here…so be gentle with me I am going to do this mode just checking how this is holding long term? are there any issue since implemented ? I will also be adding a 1N4001 1amp diode to the switch to protect the DME and toggle switch by one way restriction, please let me know.
many thanks for the above write up 👍

[Jgkram]

Danxx, sorry no one responded. The forum is not what it use to be. As far as the switches go, I have had mine in since the original post. No issues with anything as far as codes or operation is concerned. The only problem you might have is when the switches are turned on they stay on even if you shut the ignition off. It’s possible to drain your battery if you leave them on and forget them.