Hummer 2007 H3 - Manual (Page 309)

Four-Wire Harness Adapter
If you need to tow a light-duty trailer with a
standard four-way, flat pin connector, an adapter
is available from your dealer.
Use this adapter to
connect a standard
four-way 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 pin connector onto the adapter.
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