Update as promised!
Went down to BHM where Keith (fount of all Morgan Mysteries)
found that there were loose leads in a connecting block by the light switch. Juggling the connector extinguished both dip & full beam!
Coincidentally two leads then continued to the tyre sensor which might explain that instrument's intermittent fault.
The logic certainly fits so we will wait & see.
Can't praise BHM too highly
