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Thread: Electrical problem

  1. 5th September 2014, 03:20 PM #1
    rory
    rory is offline Fossicker
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    Electrical problem

    Hello,

    Wondering if someone with some electrical experience could help me solve a problem I am having.

    Vehicle: Defender 2002 Td5 wagon

    The other day, while connecting my dual batteries, I noticed the positive terminal getting hot. After some investigating I narrowed it down to the positive wire that goes to the fuse box under the seat. If I disconnect this wire and temporarily connect it to the second battery it still gets hot. I have checked/cleaned both ends of this wire - no difference. I did some more looking around and the Fuel pump relay has some discolouring on the housing from excessive heat. So now I worked out if I unplug this relay the engine continues to run and my terminal does NOT get hot anymore, but as soon as I plug it in it heats up. The wire that runs into the housing that has the most discolouring is the White/Purple wire that feeds the pump. I have disconnected the pump end and cleaned the terminals - no difference. I have used a multimeter and checked the resistance of this wire and there doesn't show any? I have switched relays around with the aircon relays in the thought that this might be the problem, but made no difference.

    Does anybody have any ideas, or tests I can try? My electrical experience is limited, so please keep it simple for me
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  2. 5th September 2014, 09:44 PM #2
    rovers4
    rovers4 is offline Master Subscriber
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    Hot wire

    I'm not familiar with the vehicle, but the heat in this case with things running, indicates that there is too much current flowing in this wire.
    What you have is called "a partial short" i.e. not enough current to melt things for this size wire.

    I think you said that it still gets hot with the pump disconnected. Therefore, disconnect the wire that goes from the relay to the pump, at the relay. You are not looking for a dirty connection, but a wire that is chaffed, or with a screw pinch, or a stray strand touching something metal that gives it a path to the vehicle ground.

    If the "hot wire" does not get hot when the relay - pump wire is disconnected at the pump - the pump is faulty.
    If the "hot wire" is still hot with the relay-pump wire is dissconnected at the relay - then it could be the relay socket, or relay internals. But I think you said that you had swapped the relays - go check the socket.

    Next disconnect the "hot wire" at the relay socket. If it goes cold then the socket is under suspicion.
    If still getting hot, then check this wire along its whole legth for chaffing/impaling etc.

    It could also be just a lug twisted around to touch another lug on this circuit.

    Hope this helps.

    rovers4
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  3. 6th September 2014, 07:13 PM #3
    rory
    rory is offline Fossicker
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    Problem Solved

    Thanks for your help mate! Great advice. Love this site.

    Ended up being two problems.

    After some investigating this morning I found the wire that runs from the battery to the fuse box (Under Drivers Seat) did indeed have corrosion through it (at the terminal end). The wire was hard, quite bumpy, and slightly melted. I missed it because it had the protective plastic sleeve over the top. Once I cut it all open it was very obvious.

    I swear my Landy feels like it is running smoother now?

    The second problem - reason the fuel pump relay was getting hot was because of a slightly corroded relay terminal connectors. Will fit a new one asap.

    Cheers,

    Rory

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