Currently my only test tool is a lighted probe.
Find a good ground like the vacuum advance unit, etc. and clip the test probe wire to it. Touch a known source of voltage like the main battery cable connection at the starter to confirm the test probe is working, and note how bright the bulb lights. This will give you a good idea when you're sensing full battery voltage, not something reduced by resistance.
Now, turn the ignition switch on and probe the coil terminal opposite the wire going to the distributor. The tester should light up as bright as it did when connected to the battery cable. If it's not as bright, you've got dirty contacts at the ignition switch, or inside it. Downstream of the coil, check the wire going to the distributor. The bulb should not light at all with the points closed, not even a dim glow. With the points open, the light should be slightly dimmer than it is on full voltage, because of the resistance of the coil primary winding. Check the terminal on the side of the distributor where the primary wire from the coil connects. It's easy to get a partial ground there that will prevent the points from switching the coil on and off. The terminal must be completely insulated from the housing, or it's like the points are closed all the time, resulting in no spark.
Jerry
