Assuming this engine has points, if you are measuring across the coil, you
will not get an accurate reading.

The + side of the coil should be hot when the ignition is on, but only when
measured to ground...NOT the - side of the coil.

The - side of the coil is connected to the points. When the points are
"open" the coil is being saturated. When the points close, the field
collapses, and make the voltage (spark).

A shorted condenser will render an ignition system useless. An open
condenser, will cause huge arcing on the point face, and can wipe out a set
of points in minutes.

Also, some models had a ballast resistor running from the primary side of
the starter, to the coil. This was used to keep the current down across the
points, during cranking.

I have always replaced my "point distributors" in all my boats, to
"pointless" electronic units...you might want to consider the same...your GM
would take an HEI replacement unit, and it is a simple swap. The coil pack
is incorporated in the distributor cap, and it is a simple two wire hook up.
One lead is + voltage from the ignition key, and the other is tach pulse (if
used).

Hope this helps some, good luck.

--
-Netsock

"It's just about going fast...that's all..."
http://home.insight.rr.com/cgreen/