Cadillac CTS Owner's Manual page 379

Your vehicle has a remote negative ( ) ground
location, as shown in the illustration. It is
located between the battery and the underhood
fuse block. You should always use this remote
ground location, instead of the terminal on the
battery.
Notice: If you connect a negative cable to the
ECM, ECM mounting bracket, or any cables
that attach to the ECM bracket, you may
damage the ECM. Always attach the negative
cable to your vehicle's remote negative ground
location, instead of the ECM, ECM bracket,
or any cables attached to the ECM bracket.
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.
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