Made some progress with this problem today.
I have always thought the headlight was a bit dim, so i bought a 50% brighter bulb. A bit of a bugger to fit it as the H4 bulb was a tight fit in the reflector.
Anyway, after much tugging, pushing and general fiddling around behind the dash, i got the bulb seated properly and got it all back together, and took it out for a spin.
Not only have i got a better headlamp, but the fuel light is now working as it should again.
My guess is that there is a loose connector behind the dash area somewhere.
That is the second loose connection i have came across now. The first was the front brake light wires, where they have used a pair of bullet connectors under the headlamp. These were in place but a rattly fit.
I think i may have to go through the connectors with a fine tooth comb and WD40 to ensure they are all seated properly. Is this normal on a Ducati? sounds reminisant of old Triumphs.