To troubleshoot an ignition module, check if there is a spark by detaching the spark plug wire. After that, hold the end of the wire close to the engine block, and ask somebody to turn over the engine. If a spark was created in the process, but the engine doesn't work, it may be a sign of a plug problem or an issue with the ignition timing.
A weak or yellow spark is also a sign of an ignition problem. The ignition module is faulty if the spark doesn't appear at all. If an ignition module that uses points doesn't produce a spark, take out the starter drive, flywheel and breaker points cover. Inspect the points, and make sure that there is no pitting, dirt or moisture between the contacts. If a module that uses points is operated by a plunger, take out the points and the condenser, thoroughly clean everything, and install new bushing, plunger rod, points and condenser.
If an electronic ignition system doesn't produce a spark, inspect all the wires in the ignition to make sure that they are connected, and check if the air gap is not too small or large. If no problems were detected, install a new electronic module. If a battery ignition system doesn't produce a spark, make sure the battery has enough power, and charge it. Perform the same troubleshooting procedures if a weak spark is produced.