Single Wipe Function Kaput

A little niggling problem is causing me annoyance and I wondered if it is a common fault and another entry onto the 'live with it' list or if I'm being a bit of a plank...

When pressing down the windscreen wiper stalk to engage a single wipe...nothing happens. If you press and hold it...the wipers take off at great speed and then stop as soon as you release the stalk...

What have I broken now

The fault is in the self parking circuit in the wiper motor. Either the contact which supplies power until the wipers have reached their parked position is not functioning or there is no power getting to the motor.
First check that there is 12 volts getting to the motor at all times when the ingnition is on. If not then it is the switch which is in the circular metal gear case on the motor. I think it comes off by removing just three screws.
My guess is that it doesn't park properly even when operated by the other switch.

Eminently sensible suggestion dear boy; thank you. All I need now is a multi-meter and a companion...!