> As far as the "ballast resister" goes, I'm kind of Old
> School, but I thought
> it was there to limit the current (voltage?) through the
> ignition system
> when the key was in the on position. This lengthened the life
> of the breaker
> points. When electronic ignition ( no points) came in, the
> ballast resister
> was done away with.
Although it's function is to limit current, external ballast resistors
really came into play as part of US emissions modifications. The
modifications made the engines harder to start, and having an external
ballast allows the ballast to be shorted out during starting, for a hotter
spark (when battery voltage is low).
The earlier coils had the current limiting function built into the coil
(making them "internally ballasted").
The change happened during the TR6 run, between 72 and 73 model years as I
recall. Stags started out with external ballasts in 71. I don't know when
the Spitfires changed, but I'm reasonably certain they did. All earlier
Triumphs used internally ballasted coils.
All modern electronic ignitions have the current limiting function built
into the ignition, so require coils with no ballast (either internal or
external). The exception to this rule is some (not all) of the "points
replacement" type electronic ignitions (eg Pertronix Ignitor, Crane XR700,
Lumenition, Allison, etc.) DO require a ballast, which can be either
external or built into the coil. It's important when installing an
electronic ignition to use the right coil with it, especially since some of
the "points replacement" units will overheat and burn up without resistance
in the circuit.
Randall
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