Your findings are correct. The anti-runon valve is energised by receiving
12v from the ignition switch when you turn the key from 'run' to 'accessory'
or 'off'. The valve opens (or more correctly, diverts suction in the
charcoal cannister from the atmosphere to the carb float chambers) and sucks
the fuel out of the carb jets, starving the engine of fuel and stopping any
running-on. The ground for the valve comes from an oil-pressure switch
which is closed while the engine is running. When the engine stops, oil
pressure slowly drops, and when it drops below about 8psi the switch opens
so de-energising the valve. You may have noticed a click coming from the
car a couple of seconds or so after the engine stops. If this oil pressure
switch has failed, or the wiring is grounding somewhere, the anti-runon
valve could be energised all the time the car is parked which is Not A Good
Thing.
However your battery drain may be caused by something else. If you remove
the battery ground strap and connect a test-lamp in its place does the lamp
glow? If it does, and all doors and boot/trunk are closed, then you have a
drain, the brightness of the lamp indicationg the amount of drain. You can
now pull fuses and connectors, glancing at the lamp each time, to track down
the source. If a drain can have a 'source'.
PaulH.
----- Original Message -----
From: <Speedo79@aol.com>
To: <mgs@autox.team.net>
Sent: Sunday, January 23, 2000 1:02 AM
Subject: Ignition Switch Help!
> Listers,
>
> My 1977 MGB has been slowly draining its battery overnight. I have been
> checking all the possible switches when I got to the ignition switch.
> Could someone please tell me what circuits of this switch should be hot
with
> the key off and with the key in "accessories" mode? Right now my switch
> shows continuity with the radio (white with green tracer) circuit and with
> the running-on control valve (slate) with the "accessories" on, and the
> running-on control valve circuit is hot with the key off (but only about
.6
> ohms, as compared to 1.8 ohms with the accessories circuit on-as tested
from
> the brown "always hot" wire to the slate wire).
>
> Also, what is the function of the running-on control valve? When is that
> circuit supposed to be energized, and when is it not supposed to be?
>
> I know these are technical question, but I am very thankful for all of
your
> help.
>
> Steve Sanchez
> 1977 MGB
>
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