Car info always of interest and sometimes relevant.
Windshield washer motor receives its power from central timer module and the operation of the wash function on the wiper/washer switch provides the ground to complete the circuit and cause motor operation. A ground on the P/W wire between the connector at the motor and the wiper/wash switch would cause the symptoms you are experiencing.
Disconnecting the 11 pin connector at wiper/washer switch should not affect the rogue operation if a ground the cause. If rogue operation ceases then internal switch fault would be prime suspect. Terminals 10/11 are wash motor contacts and should not conduct until wash switch operated.
As a precation battery to be disconnected for at least a minute, before working on steering column, to ensure air bag back-up power is discharged. Battery must be reconnected and ignition on to test washer.
