A 76 should have an ignition relay, and with a new alternator the North
American wiring (UK is done differently) will likely give this problem.
What happens is that the ignition warning light (and the fuel pump) on North
American cars with an ignition relay is wired directly to the white i.e. the
ignition switch and hence the coil of the ignition relay. The leakage
through the warning light from the 14v on the alternator field connection
(with the engine running) seems to be enough to hold the ignition relay
operated and hence the engine running (that is, normal running not
Dieseling) when the ignition switch is off. You may find that as soon as
the fuel pump gives a click the relay will drop out and the engine will
stop, but that is only a theory. The usually recommended fix is to install
a diode in series with the ignition warning light such that the light still
glows when the ignition is first turned on, and this will stop the reverse
leakage from the alt through the lamp to the relay.
UK cars have the warning light, and the fuel pump, connected to the contacts
of the relay i.e. the white brown even though these two items still have
white wires running to them.
Since this is such an obvious problem I can only assume that the original
alts did not allow sufficient leakage to hold the relay operated whereas
current (!) ones do. Either that or the relay with age has a tendency to
'stick' with the leakage current whereas it didn't when new.
PaulH.
----- Original Message -----
From: Dave <hearts@radiks.net>
To: MG Digest <mgs@autox.team.net>
Sent: Sunday, May 14, 2000 5:44 PM
Subject: Lucas Says Keep Running!
> Sir Lucas has struck right when I thought I had all the electrical
> straightened out. Heres the deal. Turn the key to on the ignition
> light comes on. Turn to start,car starts fine. Let run. Turn key back
> off and car keeps running. Have checked all wiring harnesses for shorts
> before and all are ok Car has new alternater. Fuse box contacts are
> all cleaned. Now this? Any ideas appreciated.
>
> Dave Ciaccio
> '76B
>
>
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