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Thread: "Back up" relay

  1. 14th May 2015, 11:33 PM #1
    alexturner's Avatar
    alexturner
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    "Back up" relay

    Does anyone know what this does and where it is? It looks like the low oil pressure light (which is no longer functional) on mine connects to it and I'm trying to diagnose. Any ideas?
    AlexTurner
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  2. 15th May 2015, 05:59 AM #2
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    JDNSW
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    What it does is stops the reverse light from coming on when the engine is stopped, using oil pressure to tell the engine is running.

    (I suspect the reason it exists is because there is no 'accessories' position on the ignition switch, to stop the reverse light being on if you happen to be parked and in reverse, but just listening to the radio.)

    I think it is the relay attached to the pedal box on mine, but I am not sure of this as I have never had any problems with this bit of the electrics!

    John
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    JDNSW
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  3. 15th May 2015, 09:31 AM #3
    Phil B
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    X2 John's post.
    AFAIK the relay lives behind the brake MC next to the on/off relay attached to the fire wall.
    I suspect that the bulb in your oil pressure light is blown as that circuit is normally closed ie the light should come on if the circuit or the pressure sender unit fails.
    If the reverse lights don't work with the engine running and the main gear box in reverse then the relay could be faulty.
    Phil B

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  4. 16th May 2015, 07:34 PM #4
    captainslow Guest
    This may help:-



    Cheers
    Pete
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  5. 17th May 2015, 03:46 PM #5
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    flagg
    flagg is offline YarnMaster Subscriber
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    Check the Oil pressure switch as well - it is on the drivers side of the block, near to the firewall. Single wire (yellow?) going to a plug with a rubber boot. Earthed or not depending on the oil pressure.

    My 'back up relay' is mounted on the clutch pedal box. It has an earth lead (black, mine is about 6 inches long) that will need to have a good connection for proper operation.

    Not sure if this is a modification that I made or factory standard but mine is also connected to the fuel stop solenoid, so if the engine runs the relay itself will be operating correctly. But as I said, not sure if that was just me and my memory is terrible.

    Quote Originally Posted by JDNSW View Post

    (I suspect the reason it exists is because there is no 'accessories' position on the ignition switch, to stop the reverse light being on if you happen to be parked and in reverse, but just listening to the radio.)
    Yes it is, and IIRC there is an ADR that requires it.. but I can't remember which one.
    Hercules: 1986 110 Isuzu 3.9 (4BD1-T)
    Brutus: 1969 109 ExMil 2a FFT (loved and lost)
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