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Thread: Bad Earth???

  1. #1
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    Unhappy Bad Earth???

    OK guys...,

    I have a problem with my indicators that has me nearly pulling my hair out!

    Last time I had the car mot'd the tester said I had a bad earth as my brake lights were dimming at the same time as my indicator lights.

    I've checked all the wiring and added temporary earths (using a jump lead direct from the battery), but it's still the same. I also noticed that the fuel pump speed varies when the indicators are on (again, in time with the indicators).

    Now, this could have been like this forever and I just haven't noticed, but would like to fix before the next mot if I can.

    Is it definitely a bad earth or am I looking for the wrong things.?

    Has anyone else got the same problem, had the same problem or got any ideas???

    Sean
    Too many idiots, not enough villages!

  2. #2
    Join Date
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    Southwater, West Sussex
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    2x 21 watt bulbs plus a side repeater and a relay is quite a load on the electrical system. If you are checking this with the engine not running I might expect it to happen.
    Shouldn't occur if the engine is running though.

    Craig.

    Built a Dax once, Long time ago, painted it blue, original huh...?

    http://www.cobraclub.com/gallery/showgallery.php/ppuser/714/username/craggle

  3. #3
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    Quote Originally Posted by GUMBALL View Post
    OK guys...,

    I have a problem with my indicators that has me nearly pulling my hair out!

    Last time I had the car mot'd the tester said I had a bad earth as my brake lights were dimming at the same time as my indicator lights.

    I've checked all the wiring and added temporary earths (using a jump lead direct from the battery), but it's still the same. I also noticed that the fuel pump speed varies when the indicators are on (again, in time with the indicators).

    Now, this could have been like this forever and I just haven't noticed, but would like to fix before the next mot if I can.

    Is it definitely a bad earth or am I looking for the wrong things.?

    Has anyone else got the same problem, had the same problem or got any ideas???

    Sean
    Hi Sean.
    A bad earth is only a high resistance in the circuit. Might be worth checking the positive side for a bad connection. As it effects the fuel pump i'd be looking around the ign fed side of things (possibly fuse box)
    Chris
    Ex AK427 351Cleveland T5WC

  4. #4
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    Craig,

    That is what I was thinking and was wondering if I was just going round in circles looking for something that wasn't really there. If it wasn't mentioned at the mot, then I probably would never know about it!

    I've only had a chance to test it with the engine barely idling (and obviously not charging properly as the charge light was on. -It's difficult to bring the revs up and look at the back of the car at the same time!) and it was still the same.
    I shall have to try it with the engine warmed up and see what happens.

    Thanks for the input.

    Sean
    Too many idiots, not enough villages!

  5. #5
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    Hi Chris,

    Thanks for the input, I'll check that side of things too - been going round in circles with is one.

    Sean
    Too many idiots, not enough villages!

  6. #6
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    Even tick over should be enough to hold the battery voltage up a bit whilst you are testing. It could be the supply from the starter motor or battery terminal to the fuse box not being big enough for the job or having bad connections.
    I assume the indicators, brake lights and fuel pump are separate fuses?

    Craig.

    Built a Dax once, Long time ago, painted it blue, original huh...?

    http://www.cobraclub.com/gallery/showgallery.php/ppuser/714/username/craggle

  7. #7
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    Craig,

    Yes, all on separate fuses (at least I know for a fact that the Fuel pump is and I'm pretty sure the others are too - all this is on a standard Dax loom).

    Interesting that you mention the starter cable as it has been a little slower to start recently - I'm now thinking that this is where I shall be looking next! (for bad connections etc.)

    Thanks again

    Sean
    Last edited by GUMBALL; 06-05-08 at 08:51 PM. Reason: too many beers, not enough typing practice!
    Too many idiots, not enough villages!

  8. #8
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    If you are saying that when the indicators are flashing your brake lights are also flashing dimmly, then i suggest you have a short between the supply side of your indicators and another part of your electrical system. You could try isolating the cables between the output side of the relay driving your indicators and the indicators and connecting in four test cables. that will rule out a short between one of your cables and earth.


    If you are saying when your indicators are flashing and you have your brake pedal pressed your break lights dim to a lower ligh level, that suggests an high load being drawn by your indicators, or a high resistance joint.

    To give you a real feel for the problem, i suggest some current measuerments. Idealy with a meter that will read up to 20 amps. If it is only a 10A meter make sure it has a fuse in it to prevent dammaging it. Connect that between your battery positive and your main supply, note the current drain if any, i would expect it to be zero. If you then turn on your hazards and you should get about 8 amps for four hazards, exact figure is (21x4)/12 assuming your battery voltage is 12 V. If you are getting alot higher current then there is a short down stream of your live feed from your relay driving the indicators, if you have a low current you have a high resistance joint (poor connection) and that could include an earth return.

    Measuring the resistance between the -ve (earth side) of the indicator and your battry -ve terminal will identify if you have a poor earth, (high resistance greater than an ohm, though thats a lot), you will need to make up extension leads for your meter probably and you must have everything turned off to take resistance readings.

    To check the condition of your battery with the engine off, turn on hedlights and measure the battry voltage should be about 11.6 to 12 v. Start engine and check battery voltage it should be about 14.4V if lower or higher suspect your charging system.

    Perhaps that helps, jon

  9. #9
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    Quote Originally Posted by JonnyBoy147 View Post
    If you are saying that when the indicators are flashing your brake lights are also flashing dimmly, then i suggest you have a short between the supply side of your indicators and another part of your electrical system. You could try isolating the cables between the output side of the relay driving your indicators and the indicators and connecting in four test cables. that will rule out a short between one of your cables and earth.


    If you are saying when your indicators are flashing and you have your brake pedal pressed your break lights dim to a lower ligh level, that suggests an high load being drawn by your indicators, or a high resistance joint.

    To give you a real feel for the problem, i suggest some current measuerments. Idealy with a meter that will read up to 20 amps. If it is only a 10A meter make sure it has a fuse in it to prevent dammaging it. Connect that between your battery positive and your main supply, note the current drain if any, i would expect it to be zero. If you then turn on your hazards and you should get about 8 amps for four hazards, exact figure is (21x4)/12 assuming your battery voltage is 12 V. If you are getting alot higher current then there is a short down stream of your live feed from your relay driving the indicators, if you have a low current you have a high resistance joint (poor connection) and that could include an earth return.

    Measuring the resistance between the -ve (earth side) of the indicator and your battry -ve terminal will identify if you have a poor earth, (high resistance greater than an ohm, though thats a lot), you will need to make up extension leads for your meter probably and you must have everything turned off to take resistance readings.

    To check the condition of your battery with the engine off, turn on hedlights and measure the battry voltage should be about 11.6 to 12 v. Start engine and check battery voltage it should be about 14.4V if lower or higher suspect your charging system.

    Perhaps that helps, jon
    Hi Jon

    Having seen this post has just reminded me that when i had my last MOT i had a problem with a similar thing, when i put the hazards on and i have the side lights on at the same time the side lights and the instrument panel lights all dim in time with the hazard lights. I have checked all the connections at the sidelights and indicators but all seems ok - any ideas ?
    Cheers !!
    Terry

    If It Ain't Broke Don't Fix It !!

    www.topclassphotographics.co.uk

  10. #10
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    Billericay, Essex, England.
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    OK,

    Jon / Chris,

    The problem occurs when the brake lights are on.

    findings so far...

    All earths are fine.

    Battery is fine.

    Charging system is fine.

    However, I have discovered that if I take the feed (at the fusebox) direct from another source (the one that comes from the starter motor and therefore a much heavier cable) and connect it to the feed for the indicators (the ignition circuit) the problem goes away.
    Now this circuit feeds lots of things anyway, so it's not been easy to find what's causing it.

    Or, do I assume that it's caused by the cable not being man enough for the job? (This is the original Dax loom, so I assume it was the correct cable in the first place) and replace with a larger cable. Making the assumption it has always been the same.

    Interestingly, it doesn't happen with the hazards on as they are not fed by the ignition circuit.

    What next???

    Sean
    Too many idiots, not enough villages!

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