Roger wrote:
I am looking for plans

I made a mag timer from an old transistor radio - one that had a 4 ohm
speaker. I connected two light test leads to the speaker voice coil
terminals & connected two more light leads to the radio output
transformer. The leads were commoned into their respective pair at two
remote alligator clip leads that could be attached to the magneto
terminal and ground. Tune in a noisy station & the sound can be
clearly heard only when the mag points are open. The change in sound
level (with Slick mags at least) is dramatic as the ponts close and
open.

I electrically "banged" the thing with the impulse many times without
effect, although I suppose a pair of back-to-back diodes back at the
transformer output would protect the radio circuitry under more trying
circumstances.

Jim Weir's RST thing below is more elegant but are the circuit boards
still available?