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Thread: Oil pressure gauge and sender

  1. #1
    Join Date
    Apr 2010
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    Default Oil pressure gauge and sender

    I'm troubleshooting the electric oil pressure gauge and sender in my 1970 IIA 88" petrol. I connected the gauge to a 9V battery and it seems to work, but the dark green wire on it was disconnected. I assume it goes to a power source - would an empty terminal on the ignition switch be OK?

    The sender is also a mystery. It's got 2 terminals and seems to be part # 537138, based on pictures I've found. One wire runs to the gauge. The other isn't connected to anything. It just ends in a bullet connector. Where should it be connected?

    If I have to replace the sender (I suspect it was disconnected because it just didn't work), are there any aftermarket ones that'll work? The genuine Smiths ones I've found are pretty expensive.
    1970 Series IIA
    1964 Series IIA [sold]

  2. #2
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    Jul 2020
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    The green wire is an ignition controlled fused connection , so should be connected to the fuse box not directly to the ignition switch ( white wires) . There may be another green wire in the vicinity to which it was previously connected. 537138 although having two Lucar blades, they are both connected to one electrical connection and earths through its body . Can you post a picture of the sender and is it a Light green wire with a white trace that runs from the gauge to the sender ?

  3. #3
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    Here's a photo after I removed one of the wires. It's in the foreground - light green with a brown tracer. That's the one running to the gauge.Click image for larger version. 

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    1970 Series IIA
    1964 Series IIA [sold]

  4. #4
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    Quote Originally Posted by IIA View Post
    Here's a photo after I removed one of the wires. It's in the foreground - light green with a brown tracer. That's the one running to the gauge.Click image for larger version. 

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    Certainly looks like a 537138 sender so I have no idea what the other loose wire is doing . I have a wiring diagram from a One Ten LR & that circuit just shows the light green/ brown wire connected to one of the blades on the sender with no other connections, as said it completes the circuit throw the body of the sender . I may be worth checking the sender to see if it isn't open circuit

  5. #5
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    Quote Originally Posted by roverp480 View Post
    It may be worth checking the sender to see if it isn't open circuit
    I've tested the wire to the gauge and that's good. I tried to remove the sender tonight to test it, but it is firmly stuck. I'm going to soak it for a while in penetrating oil, but given the position and shape, I doubt that'll work. Is it safe to use a torch in that location to heat it up? I can clean all the oil off the area, but I don't want to start a fire.

    It seems like my stuck bolts are always next to something flammable!

    Oh, and to verify that I'm not doing something else stupid - I assume that unscrewing the sender requires turning the nut underneath it counter-clockwise when viewed from above looking toward the ground. But pls. let me know if that's wrong.
    1970 Series IIA
    1964 Series IIA [sold]

  6. #6
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    Quote Originally Posted by IIA View Post

    Oh, and to verify that I'm not doing something else stupid - I assume that unscrewing the sender requires turning the nut underneath it counter-clockwise when viewed from above looking toward the ground. But pls. let me know if that's wrong.
    The thread is a standard RH so counter clockwise to unscrew. It only about 3/8" dia so should unscrew with a spanner on the hexagon without too much force. As you can see in the attached picture of the parts list, which may help you understand the assembly , the sender screws into an adaptor .
    Click image for larger version. 

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  7. #7
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    Thanks for the diagram - very helpful. Where did you find it?
    1970 Series IIA
    1964 Series IIA [sold]

  8. #8
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    Quote Originally Posted by IIA View Post
    Thanks for the diagram - very helpful. Where did you find it?
    Series 2A/3 Optional equipment catalogue. There are a lot of items fitted to Land Rovers that are standard in some markets but are only listed in the Optional equipment catalogue , such a S3 steering column locks. For info N.A.D.A. is North America Dollar Area
    Click image for larger version. 

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  9. #9

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    The oil pressure sender is a complicated device, and needs to be installed in a specific way to function correctly. The oil pressure gauge and sender do not use the power supplied by the instrument voltage stabilizer, unlike the fuel and temp gauges, as the power is supplied directly from the fused 'green' circuit. The same type of sender was used on various other English cars and there are several different pressure spans and thread types so not all interchange. If keeping an electric oil pressure gauge have typically replaced the gauge and sender with ones made by VDO.

    Looking at your picture, the black wire on your sender is connected to one of the two spades on the same riveted connection. It won't be a ground as that would ground the gauge power circuit.

    Bob

    Click image for larger version. 

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    From the OVLR archives:

    "Series III Oil Pressure Gauge - Troubleshooting a very odd device
    Original Author: Alan Richer (OVLR)
    The Land-Rover Series III electrical oil pressure gauge as provided is to an initial glance a very simple device - a gauge fed regulated voltage connected to a sender plumbed into an oil line.

    However (and most unfortunately) this is not the case.

    The sender internals are nothing as simple as a variable resistance - it's a variable duty cycle make/break unit that relies on slow gauge response to work at all. The sender contains a bimetal strip that is heated by a resistance element. The duty cycle is affected by the position of one of the electrical contacts (which is itself affected by the oil pressure of the vehicle).

    This is a great setup till it breaks - and decides not to make again.

    Metering the sender won't do you a lot of good - you need to watch it for make/break cycles and a test lamp might be best for this.

    A functioning sender will show up as a flickering light if a test lamp is attached across it with the engine running. The higher the oil pressure, the more rapid the cycle and the shorter the pulses.

    Diagnosing this arcane bit of British engineering isn't any more difficult than a problem with any of the other gauges, once you understand that. The issue here is that you can't simply meter the output of the sender to see if it is working - the entire circuit (gauge, sender and associated wiring) need to be connected and functional before you can ensure the sender's functionality (or lack thereof).


    First thing I'd do is to ground the wire on the sender (which is a big can about the size of a doorknob, not the little switch one) and see if the gauge reads upward/pins. If it does, then this tells us that the basic circuit is functional and we can turn our attention to the sender. If not, then you'll need to work your way back through the circuit with a meter and find out where Mr. Lucas has let you down.

    If +12 is getting to the sender and still nothing, dismount the sender from the fitting (making sure to plug the hole when you do) and examine the terminal that the wire is connecting to. I've seen these corrode between the terminal and rivet so that they are in physical but not electrical contact. Poking around with a meter at that joint may tell you what's up, and soldering the two together may fix the
    sender.

    To summarize, even though the design is at best a bit arcane there's no reason that a bit of common-sense electrical troubleshooting combined with knowledge can't get this functioning again as the designers intended."
    Last edited by siiirhd88; 08-26-2023 at 09:46 AM.

  10. #10
    Join Date
    Apr 2010
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    Default

    Thanks. I guess my next step is to figure out how to connect the gauge to the fused circuit. In the meantime, I managed to remove the sender. I think the pressure switch for the oil warning light is missing. Mine looks like this from the web:

    Click image for larger version. 

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    But instead of the switch with the single terminal on the right, there's a small bolt head there. Is that where the switch should go? Maybe someone removed it and stuck the bolt in to seal it? Here's mine. The mystery bolt is circled.

    Click image for larger version. 

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    1970 Series IIA
    1964 Series IIA [sold]

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