This article explains how to troubleshoot points or electronic ignitions with an external coil. This covers mostly no-start conditions. The only tool you will have to have is a good test light.
 Checking voltage and ground
First, perform a basic test for power and ground at the points: Distributor cap off, points open, ignition ON. Confirm there is battery voltage at movable contact side of the points set. If there is, next confirm the stationary side of the points set is grounded.
1. Connect the test light ground clip to a good ground or directly to the negative battery terminal.
- A. Turn the key ON and check for constant voltage at the positive (+) side of the coil. If this is good proceed to step 1B. If not your coil feed is broken somewhere. You can temporarily run a jumper wire from the positive battery terminal to the positive (+) side of the coil to continue testing or to see if the engine will fire.
- B. Crank the engine and check for constant voltage at the positive (+) side of the coil. If this is good proceed to step 2. If not, your secondary coil feed is broken somewhere. Some ignition systems use a different feed for crank and run. You can temporarily run a jumper wire from the positive battery terminal to the positive (+) side of the coil to continue testing or to see if the engine will fire. If this checks OK, proceed to step 2.
 Checking points/module
2. This step checks for proper points or electronic module operation.
- A. Using the same test light, check the negative (-) side of the coil while cranking; the light should flash. If it does then the points or module are working. If the light stays constantly lit, then the points are not closing or the electronic module is defective or the distributor ground is missing.
- B. If the light never comes on, then either the points are not opening, the condenser is shorted or the electronic module is defective. If the light never lights, you can disconnect the wire(s) from the negative side of the coil and test again with just the key on. The light should light, if not the coil is open.
If the light is flashing on the negative side, then the primary ignition is working, and you will need to test the secondary which basically consists of the coil, cap, rotor, plugs, and plug wires.
If all the above tests are OK, pull the coil wire out of the distributor cap and hold it 1/4" from the block with a well insulated pair of pliers and crank the engine. If you don’t see spark the coil or the coil wire is defective. If there is spark at the coil wire then you should have it at the plugs as long as the cap and rotor are OK.