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Re: Weirdo electrical problem

To: "Tab Julius" <tab@penworks.com>, <mgs@autox.team.net>
Subject: Re: Weirdo electrical problem
From: "Telewest \(PH\)" <paul.hunt1@blueyonder.co.uk>
Date: Tue, 20 Aug 2002 10:22:51 +0100
> I've run into a weird electrical problem (aren't they all, though?).
>
> I have a '78 B - the other day while driving my stereo cut out for a
second
> then came back on.  It happened once or twice thereafter.  I figured I
just
> had a loose wire.
>
> I then noticed that when the stereo is off, so are the following:
>
> - Horn doesn't work
> - Cigarette lighter socket has no power
> - Convenience interior light (that little one about the heater controls)
is off

All off the purple circuit (fused, always hot), bottom one in the main
fusebox.  Check the voltage on the brown feed to it and the purple from it.

> Further, the turn signal is acting weird - it stays on longer than usual
> then will speed up, but is never quite at the normal speed.

Green circuit (fused ignition), 2nd one up.  Any slightly variations in the
12v supply to the turn flasher or the switch and lights from it will cause
this.  However this is going to be the hardest to track down so leave it
until last.

> Finally, though I will test tomorrow - the temp gauge got REAL high -
> touching the red - while sitting in traffic, leading me to suspect the
> radiator fan wasn't kicking in, but I wasn't in a position to check just
yet.

Comes off the ignition relay.  If that had failed the engine would stop, but
check its own in-line fuse etc by linking the connections to the thermo
switch while the ignition is on.

> Things that seem unaffected:
> Headlights

Brown (unfused always hot)

> Dashboard/Instrument lights

Ditto

> Overdrive switch (it's electric)

White (unfused ignition) from the ignition switch which is fed by a brown.
(Aren't they all?)

> Wipers

Green circuit again, but a different branch from the fusebox (there are
many) to the turn signals.

> If the things that were broken were always dead, I'd just go looking for a
> short,

Shorts blow fuses and burn wiring, it's almost certainly one or more
open-circuits.

> but because it all works for the first 10 to 60 seconds, then it
> dies, I'm suspecting an electrical component is flaking out, but don't
know
> who the culprit might be.  In the morning, after it sits all night, I'll
> see if it stays on for more than 60 seconds.  In the meantime, I'm hoping
> maybe someone here with a better understanding of All Things Lucas would
be
> able to point me in the right direction.

Looks like you have several problems, just pick on one at a time and track
that down, don't go looking for a magic bullet.  Electrical connections can
be loose and slightly high resistance then go higher resistance and fail
altogether as they heat up due to the initial slightly high resistance.  I
don't see one 'component' being responsible, with the possible exception of
multiple bad connections in/to the fusebox.

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