Ignition on, ground the clip of the test light, probe to the ignition switch side of the coil. Should have voltage there. Try wiggling the ignition switch and the associated wiring to be sure there is a solid connection. Be sure the voltage is there when cranking.
Move the probe to the distributor side of the coil. With the points closed, should have 0 volts, points open should have near battery volts.
With the test light still on the distributor side of the coil, crank the engine through. The light should flash, on when the points are open, off when closed.
If the light stays on, the points are not making connection, the wire from the coil to the distributor is broken, the distributor or breaker plate is not grounded, or the distributor is not turning.
If the light does not come on, the points are closed or grounded (improperly connected), shorted condenser, wire from the coil to the distributor is shorted to ground, the coil is open internally, or the distributor is not turning.
Each time the points open, the coil should deliver a spark. A good spark will jump 1/2" or more.
That gets a spark out of the coil. Next check that the spark is making it to each plug. At the plug end of each wire, it should deliver a 1/4" spark to ground.
If the problem is intermittent, carry the test light, be ready to check when it fails.
Is this still 6 volt? Or has it been converted to 12v?
It is essential that it has the right coil or coil/resistor combination. Coil selection can be confusing. A 6v coil will have about 1.5 ohms resistance across the primary terminals out of circuit. A 12v coil will have about 3 ohm resistance across the primary terminals out of circuit. Or you can use a 6v coil and a 1.5 ohm resistor for a 12v application.
Most coils are marked as to what their application is. Don't go by the box or what the counter person tells you, check it ohms. or go by the part number on the coil. The wrong coil will give a weak spark, heat up and break down, or rapidly burn the points.
Points and condenser... A touchy subject! Todays ignition parts are all aftermarket, not near the quality that they were back in the day. Common for them to be bad out of the box, or be very short lived. Everything must be right for them to last and work properly. As said, the coil must be right. And the distributor needs to be in good order. A worn shaft bushing will not keep the points set properly, they will arc and burn.
That is where electronic conversion comes in. It is forgiving of a worn distributor, and eliminates the poor quality points. But that's all... It won't solve existing no spark issues, and it must have the proper coil resistance. It is also voltage and polarity sensitive, so be sure to specify when ordering.
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