Hummer 2005 H2 - Manual (Page 312)

Four-Wire Harness Adapter
This adapter may be
included with your vehicle
as part of the heavy-duty
trailer wiring package.
Use this adapter to connect a standard four-way
round pin connector to the seven-wire harness on
your vehicle.
Connect the adapter with the tab pointing up. The flip
cap on the vehicle’s seven-wire harness will lock
onto the tab (see arrow in the previous graphic) and
help hold the adapter in place. Plug the four-way round
pin connector onto the adapter.
4-80