It's right in there, high up, probably a bit forward of the wheel if I remember correctly. Standing looking at the open trunk from behind the car, pull back the top upper corner of the liner at it's highest, furthest back, nearest to you) point over on the side of the trunk that is to your left. It should just pull down a little, I think it flips to being almost inside out. Then reach your hand up and forward until you feel a rectangular metal box, probably 4x4x8 inches or so, (you can see it if you peer around). On the far end of it is one single flat round knob. It's the gain, and you'll want to turn it so the top rotates toward the drivers side of the car. It has a detent at 50%, where it is set from the factory, so twist it maybe half way to it's limit from there. Definitely helps.