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Thread: XJ6 S1 4.2 Butec alternator charging problem

  1. #1
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    XJ6 S1 4.2 Butec alternator charging problem

    Hi all,

    My name is Cees, I am new to this forum.
    For a while i am trying to find out why my car is not charging properly.

    I tried several options but without any luck.

    The car is a Jaguar XJ6 series 1, 4.2 litre enige and was build in 1971
    With air conditioning (at least some parts are still in there) and a Butec alternator.

    The problem:

    The alternator light stays on and the battery is not charging.

    possible solutions i tried so far:

    - Replace battery
    - Replace Butec regulator unit with a new one
    - Replace warning lamp cluster with a new old stock one

    Tests i performed
    - had the alternator tested and was told it should work fine.
    - directly connected the alternator load to the battery plus. in this case the alternator works and gives an healthy 14.4 volts on the battery.
    - rewired the battery circuit with new wires to exclude faulty wiring. in this case it still does not work.
    - bypassed the alternator lamp in the warning lamp cluster. in this case the alternator charges as it should.

    When i connect the cars wiring to the alternator the voltage drops from 14.4 volts to around 6 volts

    Of course i can build an extra switch in the dashboard to turn the alternator on or of.
    But i prefer everything works just the way it should.

    Did i overlook something?
    Do you have any advice on how to proceed?

  2. #2
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    Your tests show that the alternator, battery and regulator are all good, so the fault must be in the cars wiring. I would check all wires and connections, particularly earthing points. You say that bypassing the warning light circuit cures the problem - so I would start there.

    I seem to recall that the Butec regulators have a voltage adjustment screw - I assume that is set correctly?

    GM

  3. #3
    Senior Member rchiv's Avatar
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    Hi and welcome to the forum.
    I concur with GM on this. Only the XJ6 with air conditioning had the BUTEC regulator so if the alternator is proved then the fault must be in the regulator. Possibly an internal Diode.
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