Reverse Lights not working - Help Rewiring pigtail

Discussion in 'General IH Tech' started by rallye, Sep 27, 2017.


  1. rallye

    rallye Farmall Cub

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    Ever Since I swapped in my T-19 my reverse lights don't work.
    -From searching the forum, it looks like the Neutral Safety pigtail should become the Reverse light pigtail?
    If so, I have attached a picture of the NSS 3 wires (no pigtail exists). I do have a fresh 3 wire pigtail but I need help figuring out which wire to attach to the new pigtail yellow, green and brown wire?
    Thanks for any help!
     

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  2. RinTX

    RinTX High Wheeler

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    What kind of connector is on top of the transmission for the reverse light switch? My memory sucks but I thought mine was either a single or a double. Assuming it is a double - you have three wires. Put the transmission in reverse and have a helper watch the reverse lights as you try the wires on the different terminals to see if the lights come on. Shouldn't take long to work through all possible combinations. (Of course this assumes your reverse lights worked and one or more of those wires used to turn them on)
     
  3. stevewillis

    stevewillis Farmall Cub

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    I have an automatic transmission, so your results may vary.

    The two outside pins on the switch complete the connection to the reverse lights when the transmission is in reverse. One is the feed from the fuse panel, and the other runs to the reverse lights. It doesn't matter which direction you plug the harness connector in. The center pin is the neutral safety switch, and completes a circuit to ground (through the transmission) when the transmission is in park or neutral (again, I have an automatic). This ground closes a relay that completes a connection from the ignition switch to the starter control terminal.
     
  4. stevewillis

    stevewillis Farmall Cub

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    Sorry, I should have read your post more carefully. I see that you don't have the harness connector, and need to figure out which two of three wires should connect to your switch. My field service manual doesn't indicate wire colors for this particular circuit. Judging by photos of replacement harnesses (like this one https://www.superscoutspecialists.com/store/images/Product/large/495.jpg), the yellow and brown are likely the wires you want, and it shouldn't matter which way they are connected to the two terminals on your transmission switch. One of those two should have power with key on, and that is the feed from the fuse panel.

    Personally, I would start by checking continuity through the transmission switch with nothing connected to it. With multimeter leads connected to both terminals, you should see an open (infinite resistance) when not in reverse, and a closed circuit otherwise. Then I would measure the voltage between each of the three wires and ground with the key on to determine which wire is the fuse panel feed (I'm guessing yellow or brown). That leaves two wires to trace. One ran to your starter relay, which you presumably already eliminated or grounded directly since you are able to start your Scout now without a functional neutral safety switch. The other should run to your reverse lights.
     
  5. Scott L

    Scott L High Wheeler

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    Maybe I'm missing something, but it would seem those two circuits would be mutually exclusive. The NSS and it's related wiring circuit would only impact the starting circuit, right? Somewhere under your rig I would think there are wires that completed a circuit via some type of switch on the auto tranny when it was put in neutral. Those would be the wires to find and get connected to the pigtail that would plug onto the switch atop your manual box. At least as I can see it.
     
  6. stevewillis

    stevewillis Farmall Cub

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    Scott, my understanding is that he used to have an automatic transmission, and swapped in a manual. He now has the original wiring that went with the automatic to sort out to get his reverse lights working. The 727 automatic transmission has a single switch with three terminals, so he now has three wires. One of those wires was originally the NSS lead, which was switched to ground in park or neutral to activate a relay allowing the vehicle to start. The other two wires, when connected, power the reverse lights.

    I assume that since he is able to start his Scout, he has either bypassed the NSS relay already, or permanently grounded the trigger pin on it. So, one of the three wires in his bundle is no longer required. The task is to find the other two. He could just touch each of the three combinations of the three wires together (yellow-brown, yellow-green, and brown-green) with the key on and see which combination activates his reverse lights. However, we don't know what the NSS relay wire is connected to. If it is grounded (because he wired the relay to ground with it still connected, or because it is cut and touching bare metal somewhere), he would have a short, which is why I recommended tracing the wires with a multimeter.
     
  7. Scott L

    Scott L High Wheeler

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    Ok makes more sense now. Having only been around the manual trannies I had no idea the rev switch and NSS wiring were in the same bundle. Thanks for the clarification.
     
  8. stevewillis

    stevewillis Farmall Cub

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    Not just the same wiring bundle, but the same switch unit. It looks like the attached image. Shifting the transmission depresses the plunger to three different depths, which make or break connections for the NSS and reverse lights. It looks like ralleye's wires were cut above the single rubber boot connector that went to this switch, so we only have the wire colors, rather than positions, to figure out which two wires he needs.

    The manual transmissions don't have NSSs, right? I've been assuming ralleye will end up with one wire he doesn't need.
     

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  9. rallye

    rallye Farmall Cub

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    Thanks guys, the switch is a 2 prong pic attached and yes the 3 wire pigtail resembles the one you posted above
    w key in run position i tried all 3 wires to switch and nothing?

    Also, I know the switch works because I put the other pigtail (4 wheel) on it and the 4 wheel lit up when i put it in reverse
    just need to figure out how to wire this pigtail
    Reverse Engineer? if i were in the previous situation where i had an automatic with a 3 wire pigtail which 2 wires would i connect and which one would i tape?
     

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  10. stevewillis

    stevewillis Farmall Cub

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    If you had an automatic, you would use all three wires. The yellow and brown would connect together through the switch to power your reverse lights, and the green would ground a relay between your ignition switch and the starter solenoid control terminal.

    Do you have a multimeter? It would help if you could test each of the three wires with the key in the run position. One (and only one) should be battery voltage. That one is the feed from your fuse panel. If none have battery voltage, you should check for a blown fuse.
     
  11. rallye

    rallye Farmall Cub

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    truck starts but no reverse lights
    bulbs look new
    glass fuse is blue on 1 side? does that mean its blown?
     
  12. stevewillis

    stevewillis Farmall Cub

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    I'm not sure. Do you have a mutlimeter? If so, you can test the continuity across the fuse. If not, can you swap that fuse into another circuit with a similar fuse rating that you know is working? If that circuit suddenly stops working with the fuse in question, you know it is blown.

    If it is blown, understand the likely reason it is likely blown before you replace it. One of those 3 wires in your bundle runs to a fuse. It should be "hot" whenever the key is on. Your wires are cut and floating around. If you touch the end of that hot wire to any unpainted metal surface such as the transmission case, or if you connected it to the NSS wire in your bundle through the switch and that wire is grounded, you will have a short circuit and blow the fuse.
     
  13. SSIIbuild

    SSIIbuild Binder Driver

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    Usually in my experience the blue on one side of the fuse means it's blown. Can you see the wire in it?
    Do you have a test light or multimeter? You can easily test both sides of the fuse and see if one side is powered and the other is not to confirm its blown.
     

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