Dear Marcus,
This will be rough because I am trying to write it in time to help.
In regard to whether voltage is getting to the coil. Seems to me you
should start at the plugs and work backward. Take off a spark plug lead,
pull back the rubber boot or stuff a piece of wire up the end so it
contacts the conductor and sticks out the end of the boot, and hold it
(with insulated pliers or a thick layer of cloth) so the end of the
conductor or added wire is 1/8 inch from a head bolt. Operate the starter
(with the ignition on) and see if there is a spark.
If there isn't, reattach the spark plug lead to the plug. Disconnect the
high voltage wire from the center of the distributor cap, and repeat the
process. If you get a fat spark, then something is wrong with distributor
cap or rotor. If no spark, then the coil secondary (the high voltage
output side) is not putting anything out (or you also could have a very
bad wire between the center post of the coil and the center input of the
cap).
A basic principle for checking the continuity of the primary (low voltage)
side of the coil circuit is that current should go to the ignition side
of the primary, through the primary windings, through a wire to the
points, and (when the points are closed) through the points to ground. As
the points open and close, the making and breaking of this circuit induces
a high voltage in the secondary windings of the coil. If you connect a
voltmeter between any point in this primary circuit and ground, it should
read high (near 12v) if the circuit is good up to your measurement point
but broken somewhere downstream between the voltmeter and the point ground
(e.g. by the points being open). Voltage should be low (near 0) if the
circuit is grounded either in the normal fashion through the points or by
an abnormal short to ground, or it can be low if the circuit is bad
upstream from the place where you connected the voltmeter.
Continuing, remove the distributor cap and bump the engine with the
starter (or put trans in neutral and turn by hand) until the points are
*closed*. Connect a voltmeter between the low voltage (not the fat
central connector) coil terminal that leads to the distributor and a good
ground. It should read no voltage or very low voltage (ignition on). If
it reads 12 volts, your wire to the distributor is disconnected somehow
between the voltmeter attachment and the points, or the points are not
grounded or the points are so badly burned they are not making electrical
contact.
Push the movable point until the points are open (ignition still on, of
course). The voltmeter should read 12 volts when the points are open. If
it doesn't, then either no voltage is getting to the coil primary, or the
coil primary is open, or the wire between the voltmeter attachment and the
points is shorted to ground. Connect the voltmeter between the ignition
side of the coil primary and ground. It should read 0 or low volts with
the points closed. Open the points manually, and voltage should go to 12
volts. If it stays 0 or low, then there is no voltage to the coil or the
primary windings are shorted to ground within the coil, or there is
a short to ground between the voltmeter attachment and the points.
If it stays 12 volts, regardless of whether the points are open or closed,
the coil primary circuit is not complete to the distributor.
And so forth. Be methodical. Of course, if your friend comes
back with the new coil, stick it in and see if it works. That is what a
*professional* mechanic would do.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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