[Mgs] Alternator? problems

PaulHunt73 paulhunt73 at virginmedia.com
Sun Sep 1 04:33:23 MDT 2013


Measuring at the battery won't tell you any more than you already know, but it
won't do any harm.

If turning on the headlights made no difference to the brightness of the
warning light, or the voltages (other than them all dropping equally), then
the implication is that the alternator diodes are OK, also that the
connections between the alternator and the fusebox are OK.  However I've not
come across the test that Richard mentions, so it would be interesting to hear
what that shows.  Also compare the voltage at the alternator brown and the
alternator brown/yellow.  They should be the same, if not it does imply an
alternator problem.

Then compare the alternator brown/yellow with the fusebox white.  If they are
different then that is why the light is glowing, as it shows the potential
difference between the white and the brown/yellow.  The only way the white
should be higher is if the alternator brown/yellow is lower than the
alternator brown, which as mentioned before does indicate an alternator
problem.  If the white is lower than the brown/yellow (and consequently lower
than all the browns you have tested) then compare the brown and the white at
the ignition switch, and at its multi-plug or bullet connections (where
present), both sides.

Somewhere you must have a potential difference between the brown/yellow and
the white, at least one of the above tests should show in what area that is.

PaulH.


  ----- Original Message -----
  At the fusebox and at the alternator, I measured about 14.2V with the engine
running and revved up. With headlights on, this drops to about 13.8V. So,
clearly, the alternator is working and the connection to the fusebox is not
too bad (I measured 0.2 ohms between the alternator and the fusebox, which did
seem rather high).  Turning on the headlights on had no effect on the
brightness of the ignition light on the dashboard.


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