The front and rear roof lock motors power circuit should all be powered at the same time, so if your rear roof lock motors are running correctly then the disconnect to the front roof lock motor must be in the circuit from the roof lock solenoid to the front roof lock motor. If none of your lock motors are working then the problem could be in the control circuit to the roof lock solenoid, but if the rear are working I would check for power at the front roof lock motor when the rear motors are working. If there is no power at that time, the problem is in the harness. If there is power but no motor response, then the problem is in the lock motor. For testing, you could just power the control circuit of the roof lock solenoid and then check for power at the front roof lock motor. Another way to test the wiring harness is to check for continuity between the power terminal at the roof lock solenoid to the terminal at the roof lock motor.