Problem solved. It's the Xcom radio, it does not like 13.9 volts supplied with engine running. Have added a Pololu 12V, 2.4A step down "buck" regularor D36V28F12 and the Xcom now reads 12.1 volts with motor running. Transmitts and receives fine.
Clearly something has changed with the Xcom as the Ducati regulator output has not changed.
Perhaps the radio will continue to work with this reduced voltage, will wait and see.