All measurements are made in reference to the blue wire of the sensor. This is the common from the transformer.
You should measure about 12.5 VDC at the red and black wires of the sensor. This is how the sensor is powered. If voltage is present and the sensor is not powered, then the problem is in the sensor.
If there is no DC voltage at the sensor red and black wires, then measure for 12.5 VDC at the blue wire of the relay. If 12.5 VDC is present on the blue wire and not on the red or black wires, then the problem is in the relay.
If no DC voltage is present on the blue wire of the relay, then the problem may be an open diode or open transformer. You should measure 24 VAC on the Anode of the diode and 12.5 VDC on the cathode of the diode. If you measure 24 VAC on the cathode of the diode, then the diode is open.
During operation, the red wire of the sensor will pulse low when Occupancy is detected. This is slow enough to be measured with a DC Voltmeter. When the Occupancy Time delay has expired, then the black wire will pulse low. The RR7 version of the CM and WV sensors can be put into test mode to test this function. The switch of the RR7 WSD sensor can be used to test this function.