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Thread: Brake fail warning

  1. #1
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    Brake fail warning

    Hello all,
    My 6x6 ex-Mortar carrier has a switch on what looks like a brake circuit failure warning device. Both outlets from the master cylinder enter, and two lines exit, with a switch in between. I presume if either circuit fails, it will trip the switch. There are two wires from the switch - both black with a white trace. I measure 70 ohms between them, no connection to ground.
    Can anyone tell me please how this should be wired? The resistance of 70 ohms lights the lamp dully if I put the switch in series with the lamp. Or should I be joining these two black-white wires and using them as an earth switch for the lamp? I have VEH G273 Iss 1 but it is not clear on this.
    Thanks for any help,
    Cheers,
    Paul

  2. #2
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    its a normally open switch,

    when one circuit loses pressure the internal piston pushes one way or the other and closes the circuit.

    the switch then lights a lamp on the dash.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    TDI D1(parting/ed)
    Tdi autoManual d1 (Kept it for the girlfriend)
    Archaeopteryx 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
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  3. #3
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    Quote Originally Posted by Blknight.aus View Post
    its a normally open switch,

    when one circuit loses pressure the internal piston pushes one way or the other and closes the circuit.

    the switch then lights a lamp on the dash.
    Thanks Dave. There are two black/white wires exiting the switch. Should these be in series with the light, or will a fail cause one or both of them to ground? There is 70 ohms between these two - it doesn't change when I hit the brake pedal.

    Cheers, Paul

  4. #4
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    it shouldnt change when you hit the pedal unless theres a problem.

    I dont remember the nominal values.

    I think its power on one side, to the light from the other and then to ground... but thats only off the top of my head I'd have to dig through the wiring diagram.

    yes I have it.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    TDI D1(parting/ed)
    Tdi autoManual d1 (Kept it for the girlfriend)
    Archaeopteryx 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.

  5. #5
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    Quote Originally Posted by Blknight.aus View Post
    it shouldnt change when you hit the pedal unless theres a problem.

    I dont remember the nominal values.

    I think its power on one side, to the light from the other and then to ground... but thats only off the top of my head I'd have to dig through the wiring diagram.

    yes I have it.
    I thought that may be it, but am confused by the 70 ohms between the two black/white wires. That is enough to dully light the warning lamp.
    On the diagram I have, it shows a 'PDWA' switch but with only one wire. Unfortunately my wiring was too much of a mess to trace these leads before ripping the molten mass out.

  6. #6
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    Quote Originally Posted by Silenceisgolden View Post
    I thought that may be it, but am confused by the 70 ohms between the two black/white wires. That is enough to dully light the warning lamp.
    On the diagram I have, it shows a 'PDWA' switch but with only one wire. Unfortunately my wiring was too much of a mess to trace these leads before ripping the molten mass out.
    Pressure Differential Warning Actuator

    the 70 ohms means its probably got brake fluid in it...
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    TDI D1(parting/ed)
    Tdi autoManual d1 (Kept it for the girlfriend)
    Archaeopteryx 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.

  7. #7
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    the wirings a fit of stuff..

    but...

    power comes in through the bulb and then goes to the connector for the pad wear switch and the pressure differential warning actuator.

    it then goes to the brake check relay which energises with the starter to light the bulb as a light test function.

    your 70 Ohms may be you picking up the pad wear lead which means it may not be the switch but the pad wear wire.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    TDI D1(parting/ed)
    Tdi autoManual d1 (Kept it for the girlfriend)
    Archaeopteryx 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.

  8. #8
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    Quote Originally Posted by Blknight.aus View Post
    the wirings a fit of stuff..

    but...

    power comes in through the bulb and then goes to the connector for the pad wear switch and the pressure differential warning actuator.

    it then goes to the brake check relay which energises with the starter to light the bulb as a light test function.

    your 70 Ohms may be you picking up the pad wear lead which means it may not be the switch but the pad wear wire.
    Thanks Dave, that all makes sense. The pad wear indicators were long gone, there are just these two wires from the PDWA. I presume one should be grounded, the other connected to the cold end of the light. Do you know if the PDWA resets itself after a fault situation, or must it be manually reset?
    Cheers, Paul

  9. #9
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    the wiring diagram shows the bulb providing the power and earth coming in via one of 3 sources...

    1. the brake check relay
    2. the pad wear sensor and....

    now Ive looked at the higher res pic.

    the pdwa switch.

    it looks like the 2 wires should be NC to each other and then when the PDWA part kicks in it grounds to the body of the valve.

    in theory the PWDA self resets after the fault condition clears. sometimes they stick.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    TDI D1(parting/ed)
    Tdi autoManual d1 (Kept it for the girlfriend)
    Archaeopteryx 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.

  10. #10
    Join Date
    Apr 2013
    Location
    Bemboka NSW
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    Many thanks Dave for all your responses. I guess 70 ohms is close enough to NC between the leads, so I will just common them and connect to the cold end of the warning light.
    Thanks again,
    Cheers,
    Paul

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