On 6 Dec 2004 14:11:10 -0800, wrote:

Take out the resistor. It will run fine. One caveat. Make sure that
you do not leave the key on without the engine running. It WILL blow
up the coil. Running the higher voltage will give you a "hotter"
spark.

My dad, grand dad and I have been putting alternators on IH B and C
tractors for years. Of course all were originally 6V systems. We have
just switched them directly over to 12V using the original coil. As
long as you do not let the coil "soak" at this higher voltage it will
not adversely affect it. I am sure it does reduce the life of the
coil, but we have run then for an awful long time with out replacing
any of them. It isn't actually the voltage that is hard on it, but the
higher current that the primary windings take without the resistor
limiting the current.

As mentioned, this will result in a hotter spark. This is good. You
can run a wider gap and/or get the plugs to jump better if you are
burning oil or have likewise poor conditions.

As one other poster mentioned, you could put another resistor in
parallel to effectively 1/2(assuming matching resistor) your resistance
and bump up the primary voltage. This will work well and limit the
potential to cook the coil.

JW
Coil life may not suffer, but with point ignition, point life WILL.

As for current vs voltage - you can argue both ways. High current can
only flow through a fixed resistance with increased voltage - so which
came first - the chicken or the egg? You cannot have high current
without too high voltage - so it IS the voltage that is critical for a
given coil. The only way a ballast resistor reduces the current flow
in the coil is by reducing the voltage seen across the coil. It does
this by creating a "voltage devider". The resistor drops its share of
the voltage, leaving less for the coil.

The net effect is to reduce the current flow through the entire coil
primary circuit - including the points.