Any tips for locating a bad ground in the rear dome circuit?

Discussion in '80-Series Tech' started by AUGuy, Sep 13, 2016.

  1. AUGuy

    AUGuy

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    Almost positive I've got a bad ground somewhere in between the Rear LH/Rear RH Courtesy Switches and the Dome light.

    As so many dome light threads have gone, the rear dome will come on while switched to ON position, but does nothing when switched to DOOR. Additionally, the little panel lights at the bottom of both LH and RH Rear doors do not light up in any situation.

    I've verified all bulbs are good and both Courtesy Switches have been cleaned, tested, and put back on. Somewhere between the single-wire connection after the switches and the connector to the dome I'm losing my ground connection.

    Front dome light/front map light/front door panel lights all work as designed.

    Is there a spot in the wire routing that is notorious for losing the ground in this circuit? Am I missing something easier than following the wiring from start to finish? Not sure if it's related to this grounding issue, but I have engine interference coming in through the speakers while running.

    1995 FZJ80, no cargo dome light installed.
     
    Last edited: Sep 13, 2016
  2. FranceJohnson

    FranceJohnson

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    I have a 92 which might be different, and I can't remember exactly but...the rear dome light only comes on when the cargo door is open or the rear doors; not the front. I did some analyzing of the rear cargo light, it seems to always have a 12V supply going to it, so it turns on via a switched ground which comes from the doors. On the doors that is controlled by the little plunger switch under the black rubber boot in the door jamb, these are known the get stuck and get a bad connection over time. One of mine works normally, the other I have to touch to get the light to come on. I would start with verifying these work first. If you mess with all the switches and still nada, I would assume you would just have to trace where all 3 grounds come together, which can't be very far from the light itself.
     
  3. 82much

    82much

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    I believe the door switches ground against the body when released. I could be wrong tho. I havnt takin mine out. I am having the same issue also.
     
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  4. mrsleeve

    mrsleeve

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    I have the same issues on my 97, where the rear dome light will not trigger when the rear door/hatch are opened. I tracked it down last spring to the ground ciricut as when jumped to the front door switches to ground it works. Also swapped front rear switches and they all work.... I ran out of time that weekend and have not gotten back to it, though I seem to remember reading someplace about a ground spice for the rear dome located in the drivers foot well in the kick panel, or in the bottom of the B pillar. Let me know when you figure it out as I need to do fix this.

    Could also be a bad switch in the hatch latch from looking at the wiring diagram.....
     
  5. ReformedJeeper

    ReformedJeeper

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    I had a problem with the connector on my 97 in the rear hatch. There is a 2 prong connector that was making poor contact. Took it apart and cleaned it and it started working fine.
     
  6. Hornd

    Hornd SILVER Star

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    Exact same problem.
     
  7. Hornd

    Hornd SILVER Star

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  8. artech

    artech

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    Same issue here, and I spent quite a bit of time one weekend with the EWD and FSM trying to figure it out. No soap. Then again, I'm not the brightest bulb on the tree, but I can usually get it eventually if I just bang my head on the problem long enough-:bang:- sooner or later that wall's comin' down...

    It's probably gonna be one of those :slap: moments when it finally gets fixed...
     
  9. AUGuy

    AUGuy

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    That's correct, the door switches ground and complete the dome circuit when the door is open.

    I didn't even THINK about the latch having a switch! I'll look at it tonight. Would the latch switch being bad interfere with the operation of the rear door switches?

    That's the connector that ties into the 12V feed for the circuit. I checked mine, connection/pins all looked good.
     
  10. landcrshr

    landcrshr

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    Wouldn't interfere with the rear doors.

    For a quick test, you could try grounding the RED/YELLOW wire on that 6-pin connector to see if the dome light comes on (w/dome-switch in the "door" position). If it doesn't come on, the problem is up in the headliner some where.

    But.....
    This tells me something else is going on.

    Do you get the open-door warning light on the dash?
     
  11. kowalski

    kowalski

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    I found that the wire insulation on mine got really hard, and the end of it was broken right under the dash at the plug where it flexes the most
     
  12. AUGuy

    AUGuy

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    Yeah, I was having trouble connecting the dots as to why one bad ground would negate 2 good ones, but I'm certainly no electrician.

    I'll try grounding the connector tonight. Also, I'm not sure if I'm getting the warning light or not. didn't think to check that. I'll do that tonight as well and report back. Thanks for the help.
     
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  13. AUGuy

    AUGuy

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    @landcrshr checked the dash lights, no Ajar indicator when rear doors or rear hatch is open. Rear hatch grounds tested fine. I do get an Ajar on the front doors open. hmm...
     
  14. mrsleeve

    mrsleeve

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    same thing I have going on, I had it narrowed down to somewhere in the body harness between the drivers side rear door switch and the BCM/dash light. Likely the ground splice in that harness where ever it is
     
  15. bloc

    bloc SILVER Star

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    No. That's a fourth potential ground that can turn on the dome. (each rear door and the dome switch itself being the other three).

    Does the dome come on with opening the hatch? If so the same circuit up to the dome light itself from the door switches is fine and the problem is in the door switches or in the wires between those and the roof harness connector IE1 in the driver's kick panel.

    Per the EWD the rear door courtesy lights (in the door card) bypass other significant parts of the system.
    Even more odd is that after the junction connector that sends the +12v to the positive side of the bulb in the door card, both sides are separate circuits. One switch/side being bad shouldn't impact the other. This junction connector and +12v isn't needed for the dome to work either.. so they are a separate problem, apparently.

    My advice on what will be the most efficient? Get an EWD, especially learn how to read the connector designation codes and where to find the location of each connector on the chassis, and start checking continuity on each leg of the circuit. It sounds most like your door switches are bad. Just because they tested OK on continuity doesn't mean they'll handle enough amperage to run the light. A way to verify this is to ground the single wire to a door switch. If the dome comes on, it's your switch. Even if that isn't it, this is a somewhat complex system and an EWD is probably the only thing that will help you figure it out.

    Normally I'm glad to help interpret these things, but as I said it is a complex system with a lot of variables and there is no one problem I can find that would cause this (other than the door switches). you are probably better served learning the system and taking a systematic approach on your own.
     
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  16. landcrshr

    landcrshr

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    @bloc is right on the money. You either have a combination of two bad door switches and also bad bulbs in the doors, or it's a bad junction connector.

    Probably "J3" shown here:
    J3 Conn.JPG

    Found here:
    J3 Location.JPG

    There is a simple test you can do however that will determine which direction you should start looking.

    Open either rear door, remove the lens covering the courtesy light in the door and measure for +12 Volts on each terminal of the bulb. (+12V to chassis ground)

    No +12V = possible bad wire junction.

    +12V on both sides of the bulb = bad switch circuit.

    Full schematics here:
     

    Attached Files:

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  17. AUGuy

    AUGuy

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    I'm nearly positive the door switches are good. I tore them both apart and reconditioned them, both tested at 0ohms when in the 'door open' state from the switch to the pigtail connector. Junction box could definitely be a possibility. I'll run your test tonight and see. Thanks again for your (and everybody else's) advice.
     
  18. ThreeEyedBandit

    ThreeEyedBandit

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    It won't be the junction connector if the lights work in the 'on' position. If you have good door switches, could be the wiring between(doubtful) or more likely a bad contact in the 'switch' in the light assembly in the roof. Look there first, it's just a spring loaded ball and two pieces of brass. Common on older vehicles to have problems.

    Try removing the dome light and checking continuity from ground to the R/Y wire with the door open and closed at the light connector.
     
  19. landcrshr

    landcrshr

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    It's still possible for the lights in the doors to not work because of this, they are on separate taps of that junction. But that alone wouldn't affect the overhead light.

    I believe there's also something going on with the ground/switch side due to the "no 'ajar' light" condition.
     
  20. mrsleeve

    mrsleeve

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    I had to totally disassemble and "rebuild" my rear light switch/housing to get it to work on the bench before I even discovered there is an issue in my harness someplace.
     
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