Right - where the wire enters into the loom it feels a bit wobbly loose like the wire is broken inside after being bent back and forth too many times. I'll have a check with the multimeter now and see if it goes in and out of open circuit, would explain why fiddling around with the ignition amp and wiring (which is all cable tied up with the coil wiring) caused the engine to fire up last night only to cut out again.

Cheers,

Andy