I agree, I had the same issue, my po chopped out the ignition relay trying
to fix this problem. I spent weeks testing everything, I came to the
conclusion that it was either due to some electical load present with the
original ignition system, which modern systems, pertronix, etc did not
produce, or a surpringsly large failure rate of alternators, which would
btw charge the system otherwise. I took apart the wiring harness, replaced
every
switch, yada yada. I know some violently disagree, and I have received a
surprising amount of private emails about my polluting the mg design, some
quite disturibing actually.
I have seen referece to installing a diode in msd ignition instructions for
the same issue, and
actually several other places as well. I have to conclude that it is a
inadvertant
design defect in that year, I have had other perfectly good lucas
alternators on my car
which produced the exact same result, it is almost always +8 vdc coming out
of the indicator light terminal. a simple diode seems the most ethical and
sanitary way of resolving the issue. or adding a load.
a diode does add a .6 vdc drop to the line, which does offset the charging
point,
but that seems minor, actually I've never had a problem with that, but much
more so the high resistence of the switches etc.
I measured the current draw of my fans the other day and I was shocked as to
what an old fan draws vs a new one. that circuit needs a relay bad.
eof.
ted
----- Original Message -----
From: Rich Peterson <kerry3@earthlink.net>
To: <paul.hunt1@virgin.net>; MGS <mgs@autox.team.net>
Sent: Wednesday, June 09, 1999 8:04 PM
Subject: Re: 1977 MGB-Running on
> >>Sounds electrical, like the coil still has some voltage fed to it.
> The
> alternator, while it is still spinning, can potentially (!) feed some
> current to the coil with the ignition off. But with the relative
> resistances of the lamp and the coil this should only result in a very
> small
> voltage across the coil, insufficient to maintain a spark (otherwise
> they
> would *all* run on.<<snip>>
>
> I disagree. This problem is very common in '77s not because of a wiring
> fault but because of an alternator problem. The original alternator's
> voltage regulator protected against current feedback through the
> ignition light (and the ignition relay & coil), but once you change the
> alternator or regulator, you run the risk of introducing this problem
> unless the regulator is exactly the same as the original one which was
> installed. Since it is virtually impossible to order a regulator which
> meets the OEM spec. for the '77 MY alternator, it makes more sense to
> install the diode in the ignition light circuit. I modified mine 2
> years ago and have not had a problem since.
>
> Rich P.
>
>
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