Update. Took greywolfs advice, he's forgotten more than I know! Cleaned the earth bolt again, can't really replace it as its a crankcase bolt, only 6mm but long. Copper slipped it well up, earth good, bike startin OK. Connected the new secondary earth till bracket that supports the rear of the tank, tucked under the rubber boot over abs, other end not connected to battery, just tucked under the tool kit. So now if oe earth goes again I just connect other end till battery. Be away in 5 minutes, if I don't drop the battery screw down the back of the engine!!