On a B I'd disconnect the battery ground strap and connect an analogue
voltmeter on its 12v scale in its place. You will probably see a full 12v
(with a charged battery) displayed. Unplug the alt and if the voltage drops
to zero the alternator is indeed the cause. A good alternator will always
have some drain due to the reverse leakage of the diodes but this is
microscopic and only causes a few volts to be displayed on the meter. If
you still see 12v with the alt unplugged then it is something else, again on
a B I'd pull the purple fuse (interior lights, horn) first, then start
disconnecting browns from things like ignition switch, lighting switch etc.
but you'll need a circuit diagram where they go on a Jag, or if there are
any other 'always hot' fuses like the purple on the B.
Do you mean the tach doesn't work when the lights are on? If so that will
be the tach ground missing. While the lights are off it can find another
ground through its light and other gauge lights to their grounds but with
the lights on this path is effectively removed. If the tach doesn't work at
all you would need to check the 12v and ground supplies to it as well as the
signal from the ignition. If the dash lights don't work at all I'd look to
the rheostat first, if it has one.
PaulH.
----- Original Message -----
From: "Carl Elliott" <celliott133@comcast.net>
To: "MGs List" <mgs@autox.team.net>; "Spridgets" <spridgets@autox.team.net>
Sent: Wednesday, November 05, 2003 2:36 AM
Subject: Followed me home
> ... Battery goes dead after sitting overnight. I am leaning toward
> internal short in Alternator . Takes a while for light to go out. Also
> Tach doesn't work as well as dash lights.
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