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1987 J10 seat belt warning circuit - repair?

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  • 1987 J10 seat belt warning circuit - repair?

    I'm hoping someone here knows something about AMC seat belt wiring.

    When I bought my 87 J10, the female or buckle side of the driver seat belt was all busted up. The strap is attached to a buckle frame. Under the buckle frame is an interlocking metal thumb latch and a spring plate. All of this is housed inside the rear plastic shell. A 12v wire is still connected thru the strap and into the shell, but the shell itself is busted and several buckle parts are obviously missing.

    For now, I'm using the middle seat buckle until I fix the driver side. There is no seat belt buzzer or instrument warning light.

    Last week I found a junked 83 Wagoneer. Unfortunately the driver front buckle was busted just like mine, but the rears were in decent shape so I bought two AMC-branded rear buckles and one male latch/strap.

    Of course the rear buckles from the 83 Wagoneer don't have the electrical connector. So I started parting one out, hoping I could use the parts to fix my J10 driver buckle.

    Has anybody done this?

    I'll supply some photos in a few minutes. Here's what I've done so far.

    On my 87 J10 driver side buckle:
    The 12V wire goes from the harness behind the seat, through the strap, and into the tan plastic rear shell for the buckle. Inside the buckle shell, I found a thin piece of metal inside a white plastic holder which completes a circuit between the two lead wires with no obvious mechanical switch or mechanism to interrupt the circuit. Also, one lead wire was broken but I carefully soldered it back together and routed the wires correctly back into the buckle shell. I get continuity between the two 12v leads (which doesn't make sense IF this is a switch).

    On the 83 donor:
    I was able to carefully pull the 83 buckle apart, removing the plastic face from the rear shell. This exposed the internal components. There is no wire, of course, but the rear shell has the same internal contours to fit the wire into the housing, if one were to be supplied. The buckle otherwise has all its necessary parts in good shape.

    Is there something missing that grounds or interrupts this circuit? Am I missing any parts? Is this even a switch? Any help appreciated. I will post photos later today.
    1987 AMC Jeep J10 Pioneer 360 / 727 / 208

  • #2
    maybe wrong but just about every bulb in cluster is controlled by ground.
    meaning warning bulbs get power when ignition is on and circuit is completed on other end via ground.

    the seatbelt light is also tied into blue chime module under fusebox.
    it sends power to belt, without belt buckled switch is closed and chimes plus dash light circuit is complete.
    when belt is buckled it breaks the circuit ground = no chime, no dashlight
    88 GW, 67 J3000, 07 Magnum SRT8


    • #3
      Thanks Tony. I'm not seeing anything in the latch / buckle mechanism to ground that circuit. The latch doesn't reach the thin metal strip when snapped into the buckle. What do you make of that?

      If it's a switch, do you have any idea how it achieves that ground you're talking about?

      I'm not finding anything on the web about AMC seat belt design. I did find a couple of patent numbers on the rear shell. When I looked those up, I found an exploded diagram of the seat buckle, but it had no electronics. My 83 donor rear buckle has all the components shown in the diagram.
      1987 AMC Jeep J10 Pioneer 360 / 727 / 208


      • #4
        I've never taken one apart, generally never mess with safety item like a buckle if broken/damaged = replace entire assembly.
        kinda drilled into our brains @tech school when I went for autobody repair.

        I'll add this...1990 wiring diagram 1987 is probably the same.
        clearly shows a "switch" which is likely what's inside.
        one wire is a ground the other is from chime module.
        the buckle somehow completes or breaks the circuit.
        Last edited by babywag; 08-06-2022, 05:47 PM.
        88 GW, 67 J3000, 07 Magnum SRT8


        • #5
          Normally I'd agree but I haven't been able to find any OEM spares. There are aftermarket alternatives, tho.

          Here are some photos. Can anyone tell me whether I'm missing any electrical parts?


          This first photo shows what was left of my broken 87 J10 driver buckle, as compared to the internals of the complete 83 Wagoneer rear buckle (plus one complete rear spare):

          This photo shows how the wire or "switch" fits in the rear shell (I later fixed the broken wire):

          And this photo shows the US patent numbers, FWIW:

          1987 AMC Jeep J10 Pioneer 360 / 727 / 208


          • #6
            The 90 diagram and my 88 diagram both show a switch that is normally closed.
            meaning one wire(from chime module) is power and other is a ground.
            when belt is UNbuckled the circuit is complete and lights up dash and module chimes.

            when the belt it latched it somehow "breaks" the circuit, interrupting the ground = no dash light/chime.

            use a dvm, check for continuity @plug if you have it when belt is installed and unlatched the light should illuminate and module should chime.

            keep in mind amc/jeep changed seat belts over the years. so your 87 belt may not "break" the ground when plugged into an '83 receptacle???
            may need a later receptacle?
            Last edited by babywag; 08-07-2022, 03:11 PM.
            88 GW, 67 J3000, 07 Magnum SRT8


            • #7
              I think it may be more complicated than that. According to this thread ...


              ... the seat belt (on a 77 Cherokee Chief) has a chime on this circuit and a "fasten seat belt" warning light in the dash cluster on a 10 second timer.

              How does inserting the tongue plate into the buckle shut off the chime? I have no idea.

              I've seen references to electromagnetic and other wireless sensors, but I'm still not finding an exploded diagram for the late model SJ driver buckle with wiring.
              1987 AMC Jeep J10 Pioneer 360 / 727 / 208


              • #8
                77 doesn't have later model chime module.
                test the belt like I mentioned
                i'll wager when ubuckled the circuit is complete
                and when buckled the circuit "should" be broken.
                88 GW, 67 J3000, 07 Magnum SRT8


                • #9
                  I have no input, subscribing to see how this goes.
                  Chuck McTruck 71 J4000
                  (Chuck McTruck Build Thread)
                  79 Cherokee Chief (SOLD, goodbye old buddy)
                  (Cherokee Build Thread)
                  11 Nissan Pathfinder Silver Edition 4x4
                  09 Mazdaspeed3 Grand Touring
                  00 Baby Cherokee


                  • #10
                    I haven't reassembled it yet. Working on it, thanks guys.
                    1987 AMC Jeep J10 Pioneer 360 / 727 / 208