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Thread: Oil Pressure Warning Light

  1. #1
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    Oil Pressure Warning Light

    Driving today and the low oil pressure light came on. Does not go out with revs. Oil level is fine. Engine sounds fine.

    Is it normal for the switches to die? I read that it is strange circuit. Does someone have the wiring schematic. The thread I looked at had dead picture links.

    Is it possible to lose oil pressure suddenly on these engines?

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    Had the same once. Luckily I have an oil pressure guage and that was showing good pressure. Found it was a broken wire to the sender.

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    I found the vehicle wiring diagram. It does not make sense as it does not show power to the relay for the reverse lights. Would be to good to see if someone has figured out the details.

    Anyway, is it the relay on the firewall, next to the clutch master?

    I should say that the truck has seen some bodgy wiring from a PO, so it is always fun tracking this crap down.

    Has anyone mounted a VDO pressure sensor and, if so, some details on how it was done, would be great? I could then get one with a low pressure switch and bypass this complicated setup.

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    Quote Originally Posted by Red90 View Post

    Anyway, is it the relay on the firewall, next to the clutch master?.
    Yeah mine is down in that area, under the air intake hose from air cleaner.

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    I just fitted a normal pressure switch to mine when I did the Isuzu conversion.
    From memory that complicated system was something to do with making reverse lights only work when the engine is running.

    Steve
    1985 County - Isuzu 4bd1 with HX30W turbo, LT95, 255/85-16 KM2's
    1988 120 with rust and potential
    1999 300tdi 130 single cab - "stock as bro"
    2003 D2a Td5 - the boss's daily drive

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    Quote Originally Posted by steveG View Post
    I just fitted a normal pressure switch to mine when I did the Isuzu conversion.
    From memory that complicated system was something to do with making reverse lights only work when the engine is running.

    Steve
    Any recollection what the thread size is for the stock switch? I assume it is located below and behind the oil filter housing with two wires coming out of it?

  7. #7
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    The one on the filter housing assembly drives your oil pressure light
    the one on the block drives the reverse lights and yes, done for tactical and battery saving reasons, park nose up hill and you're supposed to leave it in reverse.

    if you need to you can rewire the sensor on the block to work the idiot light in the dash, you can also fit a secondary idiot light (basically wire a 12v feed via a resistor to a led across the block sensor wiring if it glows the switch is open so the led will light up, once oil pressure is up the led is shorted and the resistor prevents enough current flowing to light the reverse lights.
    Dave

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    Quote Originally Posted by Blknight.aus View Post
    The one on the filter housing assembly drives your oil pressure light the one on the block drives the reverse lights...
    Thanks. I will look closer but did not see a second device on the oil filter housing. The wiring diagram from the supplement shows the light connecting to a relay block and the block connecting to the switch and the reverse light. The problem is it does not show a power feed to the relay (which it would need to work). Has anyone drawn up a correct diagram of the wiring.

  9. #9
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    I think you'll find power goes to one side of the oil pressure sender. When oil pressure comes up, it switches on sending power to the relay.

    The reality is your reverse lights only work when you have oil pressure. *technically* not when the engine is running. So if the engine is running but oil pressure is not up, you won't have reverse lights.

    FYI I found the Isuzu wiring diagram correct for this. It's just tricky tracing power source to load with different switching scenarios.
    - Justin

    '95 Disco 300TDI - sold
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    So it is now fixed. The power feed wire had a break.

    What is missing in the wiring diagram is the power feed wire. It is a brown wire that runs through the engine harness to the starter.

    The relay is a dual contact relay.

    Terminals at relay.
    - Brown (unfused constant power from starter) connects to input for reverse light contact.
    - Green (to reverse light switch) connects to output of first contact. Closed when energized.

    - Brown (jumper from other brown wire) connects to coil input.
    - Slate (to low pressure switch) connects to coil output.
    - Other side of switch goes to ground.

    - White/Brown (from dash light) connect to second contact input.
    - Black (to ground) connects to second contact output. Open when energized.

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