wrote in message
...
Years ago my neighbor and I bought a 9N tractor together. we used
the
tractor for many years and then for various reasons we parked it for
several years. Deciding to use it again I wasn't able to get any
spark, even though it worked fine when we parked it. After cleaning
the points I was able to confirm that the points were properly
adjusted and making contact. Opening and closing the points by hand
resulted in an erratic and weak spark. Tracing the really simple
electrics I found that the power from the battery goes through a
ballast resistor. Unlike cars and other vehicles with ballast
resistors that I'm familiar with the ballast resistor is bypassed
during starting. But the old Ford 9N tractor doesn't do this. I
ended
up connecting the coil directly to the battery and this resulted in
a
pretty good spark. Good enough that the tractor started right up. So
why the ballast resistor? Why would the current need to be limited
for
regular operation if the ballast resistor isn't bypassed during
starting? Anyway, I am not going to run the tractor with the ballast
resistor out of the circuit because It is supposed to be there. And
before it was parked for several years it worked just fine. I think
the reason for the poor spark must be corroded connections somewhere
in the ignition circuit. But I'm still wondering why they designed
the
ignition circuit with a ballast resistor. Anybody know?
Thanks,
Eric

http://www.myfordtractors.com/index.shtml

http://www.learnabout-electronics.or.../dc_ccts45.php
The resistor AND a coil designed to generate the spark with a lower
input voltage decreases the time for the magnetic field to build up
when the points close, without overheating the coil from its internal
resistive loss.