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Inexplicable non-workage of light globes

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by ad91on, Jun 30, 2011.

  1. So I've just gone to replace the fuel lights in my Across (it has a two-stage fuel warning system, a yellow light comes on around 50kms left and a red one not long after that) as one had blown. I put in an LED wedge globe to replace the broken one. It works fine.

    I then notice the oil light goes out. Strange.

    I then take out the LED and swap it for the working fuel globe. LED keeps working, old globe doesn't. I then realized that LED's wouldn't work for the fuel warning system anyway as it works on resistance and the LED's low resistance doesn't work, much like how they don't work for indicators.

    I went and bought tradition globes today and fitted them tonight. Neither work in either socket. LED's still work. Voltmeter reading of the sockets indicates they are definitely working. Tested the new globes as well and they work. Just not in the socket.

    Same goes for my oil light. Completely bizarre.

    My one guess would be perhaps there is something creating excessive resistance in the circuit which means that there is only enough power getting through for the LED's, which still makes no sense considering the voltmeter reading or 12v for the socket.

    Any ideas? It's got me stumped.

    At least I successfully installed a 12v power socket in it though! :D

    Here is a picture which will hopefully act as stimulus for the solving of this problem:

  2. Assuming everything else is working, as you say it is, are the contact on the new globes different (different place, different spacing) to the old one/leds?

    That's all I've got, sorry.
  3. You could try adding some resistance to the circuit to make the LEDs work, not sure how much though.
  4. That's the thing, i would add resistance but it would be some major trial and error with the fuel gauging.

    Contacts are the same place... it's got me absolutely stumped.

    fuses are all good too.

    It's one big WTF.
  5. Did you turn the key?

    Sorry, I have nothing to contribute. I'm waiting on a report to get signed off at work and it was post that or "kill switch".
  6. most unexplainable electrical problems are often caused by a shithouse earth.
    having the globe/socket work in testing doesn't mean it'll work properly when you need it to
  7. Hope you have progressed on this problem ad91on. I would agree with the other posters that this type of symptom is generally poor earths. I do want to discuss this statement of yours from the OP though. Yes you are correct, remember that a Multimeter measuring volts is a high resistance so does not load the circuit. Because the circuit is not loaded the voltage across the socket will be approx 12V. It doesn't mean that there is not a bad connect providing a high resistance connection.

    :) Hope that makes sense, it is Ohms law.

    High resistance multimeter, High resistance connection, low current so low voltage drop across the bad connection. 12 volt appears across globe socket.

    Low resistance globe, High Resistance connection, high current large voltage drop across connection so low voltage drop across globe. No illumination.
  8. I seem to remember something about Ohm's law from year 9 physics, but my teacher was a bit retarded to it didn't sink in too far :p

    I haven't looked any further into this problem yet, but will be sure to let you know how I go.