What is the name of the piece of equipment that connects between the pickup and the truck camper?

The correct answer is the 12V DC umbilical cord. This piece of equipment is specifically designed to connect the electrical system of the truck to the camper, allowing for the transfer of power and providing the necessary electrical functions for the camper's amenities, such as lights and water pumps.

The term "umbilical cord" is commonly used in this context to imply a vital connection that supplies power directly from the vehicle’s battery to the camper. This connection ensures that all electrical components within the camper operate effectively while it is in transit.

Other options like the power inverter, electrical harness, or connector cable, do not provide the complete functionality needed for delivering power in the same way. While these terms may refer to components involved in electrical systems, they are not specifically designed for the direct power connection to a camper. In particular, a power inverter converts DC power to AC power, which may not be necessary for the basic operation of a truck camper, and electrical harnesses refer to a comprehensive assembly of wires for complicated systems rather than a singular connection like the umbilical cord.