Blue Wire Mod
Fleet Owner
Joined: Nov 2003
Posts: 27,881
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Add a switch to the dark blue wire in the fan connector at the top of the fan shroud. This connector is a five wire connector and the dark blue wire receives a GROUND connection from the PCM when it decides that the fan needs to be turned on. After turning on the switch to send GROUND to the dark blue wire, the viscous fan clutch heats up (it will take 20-50 seconds or so to fully heat up) and the fan will engage and run with a lot of sound!. After turning off the switch, the viscous fan clutch will still be hot, so it takes a minute or so for the fan to slow back down. Again, the dark blue wire is for GROUND only, not 12 volts! Also, the heater in the clutch draws about 1.25 amps or so. You can use a 16 gauge wire and a small toggle switch. Just make sure you do not cut the blue wire such that the PCM can't ground it when it wants to.
http://www.justanswer.com/ford/1grjp...n-off-fan.html
http://www.justanswer.com/ford/1grjp...n-off-fan.html
Thread Starter
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More Turbo
Joined: Mar 2016
Posts: 643
Likes: 6
Add a switch to the dark blue wire in the fan connector at the top of the fan shroud. This connector is a five wire connector and the dark blue wire receives a GROUND connection from the PCM when it decides that the fan needs to be turned on. After turning on the switch to send GROUND to the dark blue wire, the viscous fan clutch heats up (it will take 20-50 seconds or so to fully heat up) and the fan will engage and run with a lot of sound!. After turning off the switch, the viscous fan clutch will still be hot, so it takes a minute or so for the fan to slow back down. Again, the dark blue wire is for GROUND only, not 12 volts! Also, the heater in the clutch draws about 1.25 amps or so. You can use a 16 gauge wire and a small toggle switch. Just make sure you do not cut the blue wire such that the PCM can't ground it when it wants to.
http://www.justanswer.com/ford/1grjp...n-off-fan.html
http://www.justanswer.com/ford/1grjp...n-off-fan.html
Thread Starter
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More Turbo
Joined: Mar 2016
Posts: 643
Likes: 6
Pardon my ignorance again, but aren't the upfitter switches wired for 12v power and not ground? I haven't dug around behind them yet but can the blue wire be run directly to an upfitter switch?
Fleet Owner
Joined: Nov 2003
Posts: 27,881
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I can't recall if they have a 12v power supply to them or not. If the one you want to use does, then I would disconnect and cap it, otherwise any old toggle switch will work.
Remember, when you turn the key on, the fan will have 12v power. The PCM activates the ground to turn it on. All you are doing is installing a switched ground.
Remember, when you turn the key on, the fan will have 12v power. The PCM activates the ground to turn it on. All you are doing is installing a switched ground.
Mountain Pass
Joined: May 2015
Posts: 128
Likes: 8
From: Cottonwood, California
This isn't my work, it is a post I found a few years ago on wiring the blue wire to existing upfitter switch.
Art
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Fleet Owner
Joined: Nov 2003
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akblackfoot - I did some more looking and found that I had saved the link below in my spreadsheets:
Blue wire fan mod - Ford Powerstroke Diesel Forum
Edit -
I know I have the amp rating for the fan circuit somewhere, just can't find it yet. Anyway, I don't think a relay is required, unless you want to use the upfitter switches as they were intended.
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Lead Driver
Joined: Dec 2006
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From: So. Jersey
By grounding the blue wire at the fan clutch plug it will fully lock the fan clutch, activating the cooling fan. Not a common mod really.