here's a pic of the one i made.
i got a plug with a removeable cap so that i can use it on any type of engine whether it uses a cap on the plug or not.i cut a plug wire off a bad coil. the stripped the sheave off the wire and wrapped the wire around the base of a low heat range plug. i secured the wire with a 14mm nut i bought at the hardware store. i then put a hose clamp around the sheave of the plug wire to keep thewire from breaking where it is bolted to the plug.
then all you do is install this in between the spark plug that is in the engine, and the plug wire on the engine. so in a sense you will have two spark plugs in series. if your ignition components are working correctly, the engine will start and run and you will see spark. if not, its easy to diagnose whats wrong. spark testers can be purchased at auto parts stores too. but this is cheaper.