Here's where it goes. You need an M6 metric nut or wingnut. GM left it off (I think) because if they left it on, and somebody hooked up a large trailer with its own battery they were running a fridge on 12V, and it ran the trailer AND the vehicle battery down overnight because they were left hooked together, the owner could be stranded and cranky. Leaving it off like that makes the owner THINK about what they're doing, and what they SHOULD do is connect it by way of a high amp (30-50) solenoid that would disconnect when the ignition is turned off.