Thank you for all the responses. Here's an update.
I tried a spare spark plug wire on #1 - steady light. I tried on #2 again - steady light. I tried on #4 - flashed OK. Back to #1 - steady light. Back to #4 again - steady light. Aarrgh.
At that point I gave up for several days.
This morning, I wondered if it made a difference that the wire on the timing light between the clip-on sensor and the light was wrapped/gathered by a twist tie? Previously I left it on as I didn't need the length. I took off the twist tie and stretched out the wire....it works fine.
I'm glad it is working - but must say I feel pretty dumb!
Thanks for the help.
