After a 3 hour ride parked over night, pressed starter button and starter relay buzzed but starter didn't turn. Changed relay, starter would turn just by shorting relay terminals, worked great once and then 10 min ride and back to just a buzz from relay?

Bike has new battery so voltage should be good, but it did seem better with the lights off? so is there a connection issue on the switch side of the relay?

Any suggestions welcomed I'm a bit stumped apart from stripping starter motor for an intermittent short? which looks quite involved.

It's a K1100 ABS II from 1999

Thanks
Badger

Does the starter turn with the clutch pulled in?

Get the battery load tested, would not be the first time a new battery has fallen over.
Another possibility is a bad connection or bad contacts in the starter relay. Try starting by shorting the two big terminals on the starter relay and if that consistently works then replace the relay. You have recently replaced the battery did the old one fail and weld the relay contacts together?  If so again suspect the relay contacts, you may be able to refurbish them with some fine emery paper but clean the contacts well after as the emery grit gets embedded into the contacts and they will fail quickly again.
If you do need a new relay don't just buy genuine get back and we can help with some non OEM identical replacement HEAPS cheaper.

Thanks Rick, bought new relay as old one had been arcing seems OK again now? but I know where to look next time.