Success!
Purchased Flasher relay part number 206 from Halfords, underneeth motorbike electrical bits.
Opened instrument panel, removed lucas part from top of inside of panel.
Disconnected the unit, connected the dark green wire to the 49 connector, 49a to the light green connector and made a new earth wire from the inspection socket.
Tried right indicator - flashed very fast.
Drat.
Checked bulbs and, naturally, one had blown.
Replaced bulb and everything worked.
Connected trailer board and - - it all works!
I've just got tp tidy everything up and I'm done.
By the way, what is the trailer warning lamp for? Is it a legal requirement? And woudl a buzzer do?
FridgeFreezer, thank you.
G.