Peter R. wrote
I just received a call from my trusted mechanic early this morning.
He discovered that a capacitor failed in-flight, which in turn grounded
the mag.

This is a bit beyond my limited knowledge of aircraft mechanics and I
cannot correctly explain what a capacitor does, but the good news is
that it is much cheaper to replace a capacitor than a mag.

In case you ca

Most mag installations in modern (read - designed for electrical
systems and radios) aircraft have a capacitor between P-lead and
ground. This absorbs some of the electrical noise, and generally
reduces static on the radios.

These capacitors fail with depressing regularity, but they usually
fail 'open' - that is, they stop doing their job and radio noise
increases, but the mag keeps working. This is the first time I've
heard of one failing 'shorted' - but if one does fail shorted, you
ground the P-lead and it's as if you turned the mag off.

Glad that worked out for you - those things ARE cheap - should be
about $30 for the part and 30 minutes to change it.

Michael