My RV4, with a brand new key switch caused intermittent backfires on startup. This would shear a pin in the lycoming starter.
I happened a few times before I changed switches and I carried a spar shear pin, which was a half moon key, in my tool kit.
One time I was giving my young niece a ride from her place to our farm for a vacation. The anxious parents were standing clear and waving good bye to their child on her first flight. As luck would have it on start up it backfired and sheared the pin. I got out my tool kit, removed the cowlings, and fixed the starter. It took about 45 minutes. During that time I was sure that my brother and sister in-law were having second thoughts about this homebuilt aircraft!
I replaced that switch with toggles and did not use key switches on the eleven planes that followed it.
I have never had a problem with the toggle switched whether mags or electronic. I do a mag check at run up and always to a check at shutdown to confirm mags off.
