rear clearance light repairs

I would start from the outside checking the units for corrosion or similar. On the inside the wires run down the wall behind the bed. If you pull the separator which provides space for the Alde heat to flow you will see the wires. Using pin leads on your meter you can puncture the insulation to measure voltage (or check at the Wago connector). The lamps are LED, so a simple continuity check will not be enough. You can check for current flow if you break the connection. 2023 below.