<This evening when my wife came home in the MGA, the ignition light stayed on
<when the ignition key was turned to off. When the key was turned to on...
<the light went off. I disconected the main wire (from the battery) at the
<control box, (spark, spark) and of course, the ignition light went out. I
<plugged it back in and everything works normally?? Why?
<
<John Twist had a short discourse on the ignition light & maybe it is over my
<head electrically speaking, but how does that light actually work? no/low
<voltage:light on --> normal running voltage:light off --> high/(too much
<voltage):light on "again"???
<
<Thanks
On my TD the ignition light is connected between the generator output
and the battery (through the ignition switch). When the ignition is on
it lights whenever the generator output voltage is significantly lower
than the battery voltage (like during idle). Say the gererator is
putting out 2V and the battery is at 12V, that puts 10V across the
the light and it glows. This is a good indication that the battery
is not being charged. If the light stays on at higher RPMs, the
battery will eventually run down.
I suppose if the field contacts in the voltage regulator where stuck
closed and the other set of contacts where stuck open, it would be
possible for the generator voltage to exceed the battery voltage and
the light would again glow.
The only scenario I can think of that would cause the ignition light
to glow with the ignition switch off is if the the one set of contacts
(I think they are called the cut off contacts) where stuck closed.
This would place battery voltage on one side of the light. The
accessories connected to the ignition switch would provide the path
to ground on the other side of the ignition light. But this scenario
would also mean that battery voltage was on the generator armature
which would burn it up!
The MGA may be wired differently than the TD. So everything I said
may not apply! Let us know what you find.
Bob Donahue, still stuck in the '50s
53 MG-TD
71 MGB
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