GMC 2012 Savana Owner's Manual page 333

1. Check the other vehicle. It must
have a 12-volt battery with a
negative ground system.
2. Get the vehicles close enough
so the jumper cables can reach,
but be sure the vehicles are not
touching each other. If they
are, it could cause a ground
connection you do not want. You
would not be able to start your
vehicle, and the bad grounding
could damage the electrical
systems.
To avoid the possibility of the
vehicles rolling, set the parking
brake firmly on both vehicles
involved in the jump start
procedure. Put an automatic
transmission in P (Park) or a
manual transmission in
N (Neutral) before setting the
parking brake.
3. Turn off the ignition on both
vehicles. Unplug unnecessary
accessories plugged into the
cigarette lighter or the accessory
power outlet. Turn off the radio
and all lamps that are not
needed. This will avoid sparks
and help save both batteries.
And it could save the radio!