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Thread: Dual fans and new at this... wiring help please

  1. 06-07-2023 #1
    RootBreaker
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    Dual fans and new at this... wiring help please

    Ok so first this is for a friend who is doing this. He has a 2002 Avalanche with a 5.3L

    He is using an amazon 1999-2006 ECU Control 3 relay fan harness. With the fans wired up, he says... If he grounds out the green wire, one fan comes on high. If he grounds the white wire, both are on low.
    So it appears all is wired correctly.

    His confusion is this...
    ECU Pin 33 and 42
    Pin 33 is red and is already in use.
    Pin 42 is blue and not in use.

    Where should he hook the green wire and white wire?
    Red pin 33 to Green and white to pin 44?
    If so, do you tap into the green as we do not know what else that is going to.

    I understand that we still need to use HPTuners to enable the ECU to control the fans. Interesting the harness states that you do not need to flash the ECU...

    https://www.amazon.com/JEENDA-Electr.../dp/B09CYZCNG6

    Thanks!
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  2. 06-07-2023 #2
    DrLoch
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    High speed fan pin is RED 33, Low speed fan is Blue 42
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  3. 06-07-2023 #3
    RootBreaker
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    Quote Originally Posted by DrLoch View Post
    High speed fan pin is RED 33, Low speed fan is Blue 42
    ok thanks... have you seen it where red 33 is used and the truck didnt come with elec fans? dont know what it is connected to right now.

    cut it and splice fan wire to red then?
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  4. 06-07-2023 #4
    gtstorey
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    Get the wiring diagram for your vehicle.
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  5. 06-08-2023 #5
    Alvin
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    Quote Originally Posted by RootBreaker View Post
    ok thanks... have you seen it where red 33 is used and the truck didnt come with elec fans? dont know what it is connected to right now.

    cut it and splice fan wire to red then?
    Yes. It's used on early trucks to switch the AC from outside to re circulation. It can be removed and repurposed inside the tune.
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  6. 06-08-2023 #6
    RootBreaker
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    Quote Originally Posted by Alvin View Post
    Yes. It's used on early trucks to switch the AC from outside to re circulation. It can be removed and repurposed inside the tune.
    ok will let him know.. thanks!

    we did successfully read in the tune, change to 2 fans and write it back!!!!
    he put blue into pin 42 but he still was waiting to hear about this because AC is not working on the truck... so he is trying to figure this out...
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  7. 06-08-2023 #7
    Alvin
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    All it's used for is recirc. It wouldn't keep A/C from working.

    I can't remember if it is red 33 or blue 42 that does that.. Its the one that is often already populated in early trucks.
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