The trunk latch / power lock is the actual "Trunk light switch". There is also a rolling on/off switch on the light itself (mounted on the bottom side of the rear hat rack, inside the trunk space). But the switch on the light itself only controls whether or not the light comes on when the trunk is open, its not really a three position type switch, or it won't turn the light ON if the trunk lid is not open in the first place. When you roll that switch to the OFF position can you turn the light OFF ? Unless you're gonna pull the trunk power lock switch out of the trunk lid and get into further troubleshooting you may just have to turn the power to the light off with that roller switch on the light. At least that will save your battery.

Mike