It’s not what you think. We aren’t going to get dressed up and
preach from the pulpit but will give some help with working on
your classic or antique car. This first installment will deal
with a seldom thought of component of the points style ignition
If you have an older vehicle with points in the ignition a
ballast resistor is used to drop the voltage by about 2 volts
in a 12 volt system and also drop the amperes by about .5 amps
going into the coil. The reason a resistor is used it to
lengthen the life of the electrical components and cut down on
These resistors are usually located on the firewall with one
wire running from the ignition switch to the resistor and
another from the resistor to the positive side of the coil. If
you remove the resistor you will be replacing the points at a
much faster rate and the ignition coil more frequently.
Ballast resistors do fail and when that happens it is pretty
clear what the problem is. The engine will run with the starter
engaged but stop when the starter switch is turned to the “on”
position. Or the engine may not start at all.
Newer vehicles don’t use the ballast resistor because most use
a crank trigger sensor with one coil for each cylinder or a
pair of cylinders. The modern ignition system is also much more
And no, a ballast resistor for a fluorescent lamp won’t work.
Get one specific to your make and model. The one pictured above
is for a Chevy V-8. Others will be a sheet metal piece that
may look like an ECM to some. This concludes this session of
the Sunday Service.
Comments are always welcome.