This is a pretty sure sign that the bundle of ground wires in the trunk
aren't making good contact with the body - the pump is grounding via the
lights to the red, all the other lights and their grounds, which is enough
to make them glow but not operate the pump. Theory falls down here,
however, because turning the lights on should have removed this alternative
ground path by putting full 12v on the red, which should have put the number
plate and side marker lamps out as well as not allowing the pump to operate.
Check the voltage on various black wires, particularly the pump, wrt a good
body ground (the boot/trunk latch?) while you variously switch the lights
and ignition on. You should not see any voltage at all on those black
wires, start on a 20v scale then progressively more sensitive.
A short between red and white would not stop anything working, rather it
would put the lights on with the ignition and the ignition on with the
lights.
PaulH.
----- Original Message -----
From: Steve Shoyer <Steve@shoyer.com>
To: <mgs@autox.team.net>
Sent: Sunday, April 30, 2000 4:51 AM
Subject: Please help me find my short!
> I noticed that when I turned the ignition switch to the "On" position, the
> fuel pump was silent, but the license plate lights and side marker lights
> glowed faintly. I checked the common ground point in the trunk and it
> looked secure. I was guessing that there was a short somewhere between
the
> white circuit feeding the fuel pump and the red circuit feeding the rear
> lights, but I didn't see anything obvious.
>
> I was able to get the car started and drove it home by turning on the
> headlights, which I guessed would put (full) power on the red circuit,
which
> would somehow make the white circuit to the fuel pump work again. Does
this
> sound right, or could it be something else? Any ideas where to start
> looking for the short?
>
> Thanks.
>
> --Steve Shoyer (1980 MGB)
>
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