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Thread: 84 W900B

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    Bobtail Member
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    84 W900B

    The indicator light for my "fifth wheel unlocked" light stays on and regardless if its locked or not. Can someone point me in the right direction to finding the circuit for this so I can fix it.


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    There must be a sensor on the 5th wheel. The sensor probably provides a ground for the light. If you disconnect the sensor and the light goes out the sensor has a dead short inside. If not the wire has probably rubbed through somewhere and is grounding out against the frame/body somewhere. I'm not a mechanic but thats where I'd start.

  3. #3
    Bobtail Member
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    I'm sorry I meant to put the "fifth wheel slide unlocked". I have looked at the fifth wheel for some sort of switch but visibly I can't see one.

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    It is inside the dash, connected to the the valve that controls the slider.

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    I wondered about that, never saw a 5th wheel lock light. It should be a lot easier fix now anyways.

  6. #6
    Bobtail Member
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    Thats what i thought, I'll check their again, I tried tracing the air line off the valve and never found it. Thanks

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    Look on the valve, itself. Probably 3 ports on it, 1 in, 1 out to 5th wheel, 1 with switch screwed into it. Switch could have either 1 or 2 wires. 1 wire type grounds through the valve. 2 wire is 1 hot wire, 1 ground wire.

  8. #8
    Bobtail Member
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    Only 2 air lines, in and out, that's it.

  9. #9
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    One air line will be supply, with air in it all the time. The other goes to the slide cylinder. That one will go to the electrical switch, also.
    Your '84 KW is not much different from my '84 Autocar. Same basic set up, just a normally open electrical switch, operated by air pressure. Try tracing the wires, from the light to the switch. It's in there, just a matter of finding where they hid the darn thing.

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    Follow the line to the firewall it most likely runs to a manifold on either the inside ot outside of the firewall and that is where the switch will be

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