GMC Sierra 2018 Owner's Manual page 416

6.0L
To the generator bracket, on
the vehicle with the dead
battery.
6.6L
To the negative ( ) post on
the auxiliary battery, on the
vehicle with the dead battery.
11. Start the vehicle with the good
battery and run the engine for a
while.
12. Try to start the vehicle that had
the dead battery. If it will not
start after a few tries, it
probably needs service.
Vehicle Care
Caution
If the jumper cables are
connected or removed in the
wrong order, electrical shorting
may occur and damage the
vehicle. The repairs would not be
covered by the vehicle warranty.
Always connect and remove the
jumper cables in the correct order,
making sure that the cables do
not touch each other or other
metal.
Jumper Cable Removal
Reverse the sequence exactly when
removing the jumper cables.
After starting the disabled vehicle
and removing the jumper cables,
allow it to idle for several minutes.
415