Thanks to Don and Mike for the suggestions. The coil seens to have the vote for "most likely to fail".
I took the flywheel off yesterday to eyeball everything and make some resistance measurements. The magneto coil and ignition coil both had reasonable resistance readings. One ohm or less for the mag coil and ignition primary, 5K ohms for the coil secondary.
Then I found the condensor! Most of you will not find this exiting, but the last time I had the flywheel off to check the points on my other ped, I had not seen a condensor. Well, in typical french fashion, the condensor was mounted on the back side of the magneto, out in all the crud from road and engine, with a wire running through the plate to the coil.
The next most exiting thing was that the condensor read 5k ohms resistance. Still had a kick (some capacitance), but it should not conduct DC power.
The next, almost heart stopping event, was visiting themopedjunkyard.com, and realising that a 19.95 part + 5.00 handling + 3.50 shipping leaves me close to $30.00 out of pocket!
It is true, that in typical french fashion, the condensor is a mechanical work of art, however, where it mounts, you can't even see it.
Anyway, I have decided that the motorcycle condensor in my random parts will do, the question is, how to mount it.
Then (imagine sound of dope slap, open palm against forehead), it occured to me that I could mount the condensor next to the coil, make a short adaptor to allow the condensor to connect between the points wire and the coil. As an added feature, the condensor will now be up on the frame, away from the engine and road grime.
More to follow.