Most likely points or condenser. Check with a meter or lamp that they are opening and closing. To do that put your lamp on the coil NEG terminal and turn on the key (to run). If the points are open, or IF THEY are so dirty and corroded that they are not conducting, the lamp will be bright. Bump the engine around to get them to close
MAKE SURE you have the test lamp on coil NEG and that it is actually wired to the DIST wire
On the other hand if the lamp is very dim, the points are closed, or something is shorted in the distributor. Bump the engine to get them to open.
Properly opening / closing points will "flash" a lamp bright / dim as you bump the engine around.
A system will not spark without a good condenser. There is no sure way to test them (without special equipment) other than replacement.
Obviously the above will not work if the system is not getting power, so a couple of more tests.
With key in "run" and with points closed you should have the following voltages
At the points (coil NEG), very low voltage, perhaps 1/2 volt. The less, the better
At coil + will vary, anywhere from perhaps 5--8 volts
At the "key" side of the ballast resistor, "same as battery" depending on battery charge. Better way to check this is to place on probe on "high" voltage side of ballast, and the other probe on battery pos post. You should read a VERY low voltage, the lower the better. More than .3V (three tenths of one volt) means you have voltage drop in the harness connections
Check your CRANKING voltage. Hook one probe to the coil +, and to ground, and crank the engine USING THE KEY. You should have very close to battery voltage. A better way is to leave one probe on the coil + terminal, and hook the other to battery positive, such as the starter relay battery stud. You should read a very low voltage, the lower the better when cranking
IT IS RARE but in some distributors (usually dual point) the breaker plate might not be grounded inside the distributor. Such distributors as Prestolite cast iron dual point had a little flex ground wire as the breaker plate was on a ball bearing.
Why you would have thought that using old points is OK is beyond me. Buy yourself some new points and condenser. In fact buy TWO sets so you have spares.
CRANKING
It is IMPORTANT to understand how Mopar ignition switches work. There are TWO ignition power sources, one ONLY for "run" and one ONLY in "start."
THIS MEANS that if you crank the engine by jumpering across the starter relay you get a WEAKER SPARK than when using the key, as the ballast resistor is still in the circuit. IF the battery is low, if the points are dirty, and when the engine is very cold, or in bad condition, this can easily make the difference between starting or not.
The ignition switch is actually SEVERAL switches in one "can."
Acessory
Ignition run (IGN1)
Start
The bypass circuit (IGN2)
"Ignition run" or IGN1 is traditionally dark blue and is hot ONLY in "run." It goes dead when the key is twisted to start. This supplies the ballast resistor, dash gauges, warning lamps, and the voltage regulator
"Bypass" is hot ONLY in start. Traditionally brown, it only goes one place.........from the ignition switch, through the bulkhead, to the coil + side of the ballast resistor.
