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Thread: Headlamp issue

  1. #1
    Junior Member
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    Jul 2016
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    Headlamp issue

    Hi All,

    I did a 500 mile trip the other day in the Coupe and on the return nighttime leg of the trip the outer drivers side headlamps failed. It was not working on the low beam setting, but was functioning fine on high beam. The passenger side lamps all functioned fine.

    I took out the sealed headlamp unit the following morning and checked it on a battery - both high and low bulbs function fine.
    I then checked the fuses under the bonnet/hood and they were fine.
    I then checked the relay and it seem to be functioning fine.

    i then checked the voltage and a steady 12v appears to be to all points in the wiring and up to the plug to the headlamp unit.

    However, when I put a load (or the headlamp unit) on the wire, the voltage immediately drops to zero?
    just to recap, this is only on the drivers side 7” outer lamp and only on low beam. All other lamps are functioning perfectly.

    i am struggling to suss the problem. Any advice much appreciated!



  2. #2
    Senior Member fat controller's Avatar
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    May 2007
    Ashford, Middlesex
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    Hello and welcome to the forum

    I have no direct experience of your particular model, so hopefully someone with more knowledge than I have will be along soon. What I would say, based on experience of older cars, if you have a voltage dropping like that under load, I would be suspecting either a bad earth somewhere (high resistance), a battery that is coming to the end of its life, or a short (switch, relay, wiring), with the latter being the least likely.

    On many of these cars, the relays used for various things were the same - do you have any other circuits that use the same relay that you could swap over the relays to see if the problem moves?

    My money is on an earth at the moment.
    ex - 2002 X-Type 2.5 V6; 1995 XJ Sport 3.2; 1998 Mercedes C180 Elegance; VW Passat 2.0TDI (140); Audi A4 Avant 2.0TDI; Nissan Qashqai 1.5dCi; Current - 2007 XJ 4.2 V8 Sovereign, and occasionally an Electric Wheelchair!

    It wasn't me! A big boy done it and ran away.

  3. #3
    Senior Member FastEddie's Avatar
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    Apr 2017
    Milton Keynes
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    Hi Peter,

    If they are as I remember from my old XJ12 , there was just two fuses but with four push on spade receptacles.
    I would jiggle about the wires on the dipped beam fuse and see if it comes on , probably will be here if one side is ok.
    Measure the voltage in and out of the dipped beam fuse with the lights on , stab the wires with a point to verify.

    If it is this , the easiest fix is to put a four way Lucas box in its place with a fuse for each main and dipped light.
    You can loop the infeed and put reduced sized fuses for each lamp.
    2009 X358 LWB 2.7 Tdvi , Liquid Silver , 125k+ and going strong ......

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