I hooked up a gearbrake module, no problems. Here's the info you need:
The center solid black wire (Bl) is the ‘braking’ light.
The black/blue (Bl/Bu) wire on the left is the running light / ignition wire.
The black/green (Bl/G) wire on the right is ground.
Note that the physical layout of the wiring is different from the logical layout in the diagram.