GMC 2008 Sierra 1500 Pickup Owner's Manual page 354

The remote negative (−) terminal is a stud located on
the right front of the engine, where the negative battery
cable attaches.
5-42
See Engine Compartment Overview on page 5-12
for more information on the location of the remote
positive (+) and remote negative (−) terminals.
CAUTION:
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An electric fan can start up even when the
engine is not running and can injure you.
Keep hands, clothing and tools away from
any underhood electric fan.