Using a different ground, check for power to the socket.
If it shows power, check the ground of the socket.
If it does NOT show power, check the wires/connections/fuses that feed that socket.
Bobbo and Lin
2017 F-150 XLT 4x4 SuperCab w/Max Tow Package 3.5l EcoBoost V6
2017 Airstream Flying Cloud 23FB