V40 rear wiper problem

[Ian]

My recently acquired V40's tailgate wiper does not work, so I replaced the rear wiper motor with a tested 2nd hand one, but no joy.
There is some power coming thru' (on at least 2 or the 3 cables - I tested it with a bulb), and all other tailgate electrics work OK.

The rear wiper in meant to wipe every 10 seconds when switched to 'ON' on the stalk. Does anyone know if the relay could be the problem - and how to fix it ! ? Thanks, Ian