It's really quite simple - if you are getting no spark when moving the prop quickly over the magnet and looking at a good spark plug, your ignition is not firing. There can be a host of reasons for this - bad battery, switch, bad cable, bad ignition, etc. Generally speaking, 3W ignitions are quite resilient, as they are capable of working with higher voltage than most ignitions.

Before getting a replacement ignition, why not send this one to one of the 3W service providers and see if they can fix it for you? I get very good service and quick turnaround from Aircraft International.