Checking the ground lead for the lock button

Check the switch at license plate lighting lamp housing terminal #3 and at lock unit terminal #4. Check the intermediate cable for an open-circuit.

Remedy as necessary.

Other information

To expose the lamp housing for the license plate lighting, see Bulb, number plate lighting, replacing
To access and replace the lock button, see Lock mechanism, tailgate, replacing
Checking wiring and terminals .

Fig 1: Identifying Connector Terminals

Courtesy of VOLVO CARS OF NORTH AMERICA.

Fig 2: Identifying Ohmmeter

Courtesy of VOLVO CARS OF NORTH AMERICA.

Fig 3: Identifying Connector Terminals

Courtesy of VOLVO CARS OF NORTH AMERICA.