Honda Pioneer 1000 2017 Owner's Manual page 86

(SXS1000M3L/M5L)
socket cap
accessory power socket
To use the accessory power socket, the engine must be running.
NOTICE
Using any heat-generating accessory or improperly rated accessory
can damage the socket.
Remember to close the cap when you are finished using an
accessory, and keep water or other fluids away from the socket.