Help wiring up dual electric fans. . .takeover project???

Discussion in 'Shop - Electrical' started by atomicjoe23, Jun 22, 2010.

  1. atomicjoe23

    atomicjoe23 Well-Known Member

    Joined:
    Feb 2, 2008
    Location:
    Silverdale, WA
    I'm finally just about done with my first from the frame up vehicle. . .a '49 Jeep Willy's Pick-up and the last thing I have to do is wire up the electric fans and I need a little help.

    Here's what I've got. . .a set of electric fans that had been previously wired together and apparently ready to be hooked up to the wire harness, but weren't ever hooked up and an aftermarket wiring harness.

    The two fans are wired together and there is a relay. . .right now I have two wires from the fans that need hooked up to the harness (I've already got the grounds connected to the frame and one wire hooked up to the temp. sensor in the radiator. . .still need to hook up the ground for the sensor though). . .I'm pretty sure that one wire will supply power to relay to shut the switch in the relay and the other is to complete the circuit once the switch is shut. . .I'm thinking that the thicker (red) wire is the main power to the relay and the thinner (green) wire is to complete the circuit???

    . . .where I'm confused is where each of these should hook up to the wiring harness. . .I only have one wire that is labeled for a fan (there is another wire that is labeled for the electric temp. sensor but I don't think I will be using that one since my water temp. gauge came with it's own sensor).

    Where should I hook up the red wire and where should I connect the green wire???

    I know this is kinda vague and I can explain a little better if needed, but I thought some of you guys would be familiar enough with this stuff to understand what I was talking about and be able to help me out.

    Thanks!
  2. atomicjoe23

    atomicjoe23 Well-Known Member

    Joined:
    Feb 2, 2008
    Location:
    Silverdale, WA
    I guess I'll clarify a little right now while I'm out. . .

    . . .I've hooked up a ground for each fan and a ground for the relay itself, and I've also hooked up a single wire to one of the terminals of an electric temp. sensor in the radiator. . .

    . . .leaving me needing to connect a ground from the radiator temp. sensor to the frame (or should the other terminal be connected to the electric temp. sensor wire of the wiring harnes???), one small (power???) wire, and one larger (main power to the relay???) wire.

    Thanks!!!
  3. loufish

    loufish Member

    Joined:
    May 7, 2005
    Location:
    Burbank, CA
    It sounds like the red wire is the Batt+ and the green just might be the ground for the relay going thru the temp switch...You can wire up relays several ways...I like to provide power to the control side of the relay and switch the ground of that circuit to turn it on & off...
    A couple of things....Many fans draw a lot of amps, depending on size expect 30-40 per fan so make sure the relay (or relays...) are up to the task...Second, I always wire in a manual switch switch so the fans can be controlled other then the temp switch...
  4. atomicjoe23

    atomicjoe23 Well-Known Member

    Joined:
    Feb 2, 2008
    Location:
    Silverdale, WA
    So. . .you are saying that the larger red wire is probably supposed to go to the battery and the smaller green wire should be connected to the radiator temp. sensor/switch?

    Thanks!!!

    Greatly appreciated.
  5. Co-Dog

    Co-Dog Active Member

    Joined:
    Mar 13, 2007
    Location:
    La Mesa, CA
    Pull the relay. There should be numbers next to each terminal. Bosch and all Euro style will have these numbers: 85,86,87,87a,30.

    You want the relay to deal with the current inrush of the fan motor, so you use the sensor switch to operate the relay. If the sensor is a 2 wire switch, then ground one of the terminals and take a wire from the other sensor terminal to 85 at the relay.

    86 needs to go to the ign. side of the fuse block with a small fuse, 3-5A is fine, or connected to something that gets power when the ignition is on.

    If you want a sensor override switch, you connect one side of the switch to ground and connect the other to 85 at the relay, the sensor, or somewhere in between. That's all the wiring you need for the control side of the relay.

    The fans wire to 87.

    30 gets a fused +12v from the fuse block. The fuse primarily protects the wire and the relay, and secondarily, the fan. It cannot be bigger than the rating of the relay or the wire. Hopefully, you've got #10 wire and the relay is at least 30A. Max. fuse would be 25. You really need to know the specs. on those fans. It's likely that both fans draw more current than the relay can handle. I recommend a second relay regardless. The second relay only needs a fused +12v from the fuse block to 30 and the + from the second fan goes to 87. 85 and 86 jumper to the first relay.

    Hope that helps
  6. atomicjoe23

    atomicjoe23 Well-Known Member

    Joined:
    Feb 2, 2008
    Location:
    Silverdale, WA
    Thanks Co-Dog. . .that will be a big help. . .I'll double check the previous wiring when I get home!
  7. ProFORMANCE

    ProFORMANCE Active Member

    Joined:
    Nov 16, 2006
    Location:
    Orange County, CA
    Co-Dog is "Spot On."

    Follow his instructions and you will be good to go.

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