GMC 2004 Yokon Denali Owner's Manual page 316

Four-Wire Harness Adapter
Use this adapter to connect a standard four-way round
pin connector to the seven-wire harness on your
vehicle.
4-66
This adapter is included
with your vehicle as part of
the heavy-duty trailer
wiring package.
Connect the adapter with the tab pointing up (see
arrow). The flip cap on the vehicle's seven-wire harness
will lock onto the tab and help hold the adapter in
place. Plug the four-way round pin connector onto the
adapter.