I would try connecting a wire to the solenoid (in addition to the wire that should be there from the ignition signal) and when it happens again, touch that wire on the positive battery to see if the starter goes.
If there are two of you, one could measure the voltage on the second wire when the ignition key is turned - a low or zero voltage could highlight some issues.
Can't remember if you changed the spade connector on the wire from the ignition to the solenoid?
Thanks for yor help Ringo, no not changed the spade but I crimped it up so it was tight on the terminal, its original but looked good to me. I wonder if I had the long wire going to the solenoid like you said, but permanently hooked up to a voltmeter in the cab.
Hi Ringo its ongoing I have found if I rock the ignition back and forth 4 or five times it will eventually fire. bigger fish to fry at the mo I spit a coolant hose the other day.
I've got a original ignition switch here that I bought to solve the very same problem. However, mine was just a dirty spade connector so I never fitted it.
Anyway, if you want it, pm me your address and i'll stick it in the post.