Hi Richard, just as an aside, if it turns out it is related in any way to the coil packs. I have two brand new Hella coil packs you can have, they are a left over from my touring spares for our ex 2016 3.7 Roadster.
Dave

Dave
Plus Six "Squeak"
Roadster departed.
1936 BSA Empire Star Q8. 1935 BSA W7-35. 1938 BSA M20