Which component is not part of an auxiliary source connection?

The component that is not part of an auxiliary source connection is a visual pressure indicator. Auxiliary source connections in medical gas systems are designed to ensure that there is a reliable backup supply of gas to the system. These connections typically include components that manage the flow and isolation of gas, such as valves, tees, and removable plugs or caps.

A visual pressure indicator, while it is an important device for monitoring pressure levels within the gas system, does not directly contribute to the connection or integrity of the auxiliary source itself. Instead, it serves a different function—providing visual feedback about the pressure of the gas in the system, which helps personnel monitor the system's operational status. However, it is not a structural component involved in the physical connection of the auxiliary source. Thus, it is correctly identified as not being part of the auxiliary source connection setup.