Ed,

Grounding the coil to the engine case through a switch is an important safety feature. I use a good size toggle switch on the forward side of the fuselage that is easily accessible. You never know when you will need it. A remote kill switch is even better, but I have to admit I generally don't use them (part of being cheap). I wished I had one some time back when I had a runaway engine. Stuck on full throttle. Handling was not a problem, but my endurance was. That little 21cc gasser didn't suck much fuel. The problem started about 5 minutes into the flight. About 45 minutes and one relief pilot later she came down uneventfully deadsticked. In today's commonly over-powered birds, a stuck open throttle might be a much bigger challenge to handle - safely, and survivably.

Have fun,

Bedford