Switch question for rear defroster

Discussion in 'Electrical and Ignition' started by Syleng1, Nov 30, 2018.

  1. Syleng1

    Syleng1 Karma is real and Life is short... FABO Gold Member

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    Does any one know if there is an electric factory switch like this but just on and off?
    This one is on, on, off. 3 terminals- hot, load 1 and load 2.

    If yes- what’s the application?
    Need it for a rear defroster for a 66’ Barracuda project. image.jpg image.jpg
     
  2. 65 Dartman

    65 Dartman FABO Gold Member FABO Gold Member

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    The factory map light switch is just as you described - off or on. I was under the impression that the rear defogger was a 2 speed unit, so the switch would be off, on1 and on 2. I have a couple of rotary rear defogger switches I'm using in my 47 Dodge project and they are set up the same way as your defogger switch - off, on 1 and on 2
     
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    • 67Dart273

      67Dart273 Well-Known Member

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      Page 8-157 of the 72 service manual, which you can download for free, from MyMopar Some of those manuals there came from the guys right here
       
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      • Syleng1

        Syleng1 Karma is real and Life is short... FABO Gold Member

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        Thank you 65 Dartman. You are right on track. The system I’ve cooled together for this 66 Barracuda (SN: the holy grail of options for 66 barracudas) is only single speed unless you have the resistor. On my 72 Demon the resistor is part of the blower motor. On a Barracuda I have the wrong switch or the 2nd speed is not used. Gonna make it single speed.
         
      • toolmanmike

        toolmanmike FABO Staff Staff Member FABO Gold Member

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        Factory defrosters had a 2 speed fan. There is a resistor coil at the motor that some think is a heat coil.
         
      • 4spdragtop

        4spdragtop FABO Gold Member FABO Gold Member

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        My 67 factory defrost is 2 spd.
         
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        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          The 66’ a body for the Barracuda may have been 2 speed. But the resistor is not mounted on the blower motor like the 67-76 model. Because they are so rare - very few people actually have that info.
           
        • LJ67barracuda340

          LJ67barracuda340 Well-Known Member

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          My 67 Cuda has a resistor wire from the "on 1" position on the switch to the motor, no resistor at the motor. When I rewired the whole car I only had high blower speed so I had to find the resistor wire from the old harness.
           
        • toolmanmike

          toolmanmike FABO Staff Staff Member FABO Gold Member

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          Capture rear defrost.JPG
          I have a NOS defroster kit. I wonder what it has? I also have later model parts without a switch and harness that does have the resistor.
           
        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          That’s interesting! I’d love a picture of the resistor if available.
          Joe
           
        • LJ67barracuda340

          LJ67barracuda340 Well-Known Member

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          No can do, the wiring is buried in the car now. I used the wire harness part of the original from the front switch to the rear motor. Checked it and re taped it. When I plugged it in though I magically had two speeds. One thing I forgot to do was check the resistance of the two power wires.
           
        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          I was thinking about just using a ballest resistor for low speed. Safe and works well .... okay need to test if it works but should do the job. Thanks for the advice.
           
        • halifaxhops

          halifaxhops It's going to get stupid around here! FABO Gold Member

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          • 67Dart273

            67Dart273 Well-Known Member

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            Get a 4 pin. You can wire it in different combinations to get the speed you want......

            1....high resistance side only
            2....low resistance side only
            3....wire both in parallel will give you lowest resistance
            4....wire both in series will give you most resistance

            Be sure to wire it so it gets cooling and is away from combustibles they will run HOT!!!
            I was thinking that the defroster mounted the resistor in the airstream, somehow, maybe the intake to the blower?
             
          • Syleng1

            Syleng1 Karma is real and Life is short... FABO Gold Member

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            Because of where the blower motor is mounted. A single coil ballast would work for the low side well if I just put it inside the area above the wheel well behind the outer quarter panel.
             
          • toolmanmike

            toolmanmike FABO Staff Staff Member FABO Gold Member

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            I un boxed the one I have and I only see 1 feed wire to the blower motor but the switch is a 3 position. (on,off,on or off 1-2) I am in the middle of Christmas decorating right now. If I have more time in the next day or so I would like to get out the multimeter and do some testing. I don't see any mention in the instructions about that either except it does say to dress the wire from the switch. (not wires).
             
          • 67Dart273

            67Dart273 Well-Known Member

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            The problem is I have no idea whether the resistance is correct. What you need is one of these hoarders on here LOL to measure one they have that is for the defroser

            Used to be parts stores sold "volt drop" various names intended for 6/12 conversions. If memory serves, one popular "round" device was designed to drop 12 to 6 WHEN USED with a 4A load. The motor load and the resistance both determine how fast it will go, along of course with supply voltage

            The put this simply it's called "Ohm's Law"
             
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            • toolmanmike

              toolmanmike FABO Staff Staff Member FABO Gold Member

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              Instructions. 20181201_151509.jpg 20181201_151509.jpg 20181201_151445.jpg 20181201_142001.jpg
               
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              • Mike69cuda

                Mike69cuda 63 is the new 17 FABO Gold Member

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                You could just tie two of the Switch terminals together if you want it to run on high only. Then it ,would be off-high-high and cost no money....
                 
              • Syleng1

                Syleng1 Karma is real and Life is short... FABO Gold Member

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                That’s a great idea- but I’m kinda funny like that. If it is going to work it has to work right. I’ll never use it but it has to work if I ever do.
                Lol!
                 
              • Syleng1

                Syleng1 Karma is real and Life is short... FABO Gold Member

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                JC Whitney sells those. Not sure if the motor pulls enough amps to lower the voltage to make a difference. bUT a ballest resistor creates heat to drop voltage. Not hot enough to damage but I’m going to try that route first before since I have 1/2 dozen in the shop. Thank you for the Info. Different way to look at it.
                Joe
                 
              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                20181202_083543.jpg
                I can get you a resistance for the dropping resistor. BRB.
                 
                Last edited: Dec 2, 2018
              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                I get 4.2 ohms
                 
              • Mike69cuda

                Mike69cuda 63 is the new 17 FABO Gold Member

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                You can estimate the resistance pretty easily. For instance, if it is a 12 volt supply and you measure the run current with a meter and it is 2 amps, the 12 v divided by 2 amps, that means the motor has an effective resistance of about 6 ohms. For starters, if we add 2 ohms (about 30%) that reduces the current to about 12v divided by 8 ohms which is about 1.5 amps. So you have reduced the current by 25%. The motor speed isn’t exactly reduced by 25%, but it is a good ballpark way to start.
                 
              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                See post 22 and 23