Check central locking of SEAT Ibiza 2003 6L1

I have a 2003 Seat Ibiza model 6L1 and the central locking of the driver's door is not working. I would like to know if it is the wires feeding the locking motor or if it is the motor that is not working. I would like to know where to measure voltage to know if it is the motor or not. And then I would like to know how to check if the motor is ok.