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Good morning, I hope I can help you.
If the motor is working ok when bench tested then faults could be :-
1. A faulty fuse.
2. A faulty switch.
3. Faulty relay or control unit.
4. Faulty wiring.
5. A faulty earth connection.
You have to start at the rear because you know the motor is good. Make sure it has a good earth connection. Now check fuse is ok.
Use a multimeter or testlamp to see if motor is getting power when switched on.
If no power shown work towards the front following the wiring route and check at regular intervals to see if power appears which would indicate break in wiring.