Here is why I asking which is the ground wire: I purchased a device that will make your third brake light blink when you hit the brakes to better get the attention of drivers behind you and alert them that you're stopping. Going with the assumption that the green striped wire was the ground, I installed it following the instructions, pictured here:
After installing it, when I press the brake, the third brakes on just goes on normally and never flashes. Before I go cutting any more wires, I'd like to know if I had the wires backward, or if my device wasn't working.
I'm also wondering if the fact that the third brake light in the wrx spoiler are led might also be the cause of the problem. here is the link to the product website: