Interesting, it says "bracket to be attached" so if that's a requirement I assume it goes to chassis and provides a ground for the internal circuitry.

Mach1Driver wrote:

Interesting, it says "bracket to be attached" so if that's a requirement I assume it goes to chassis and provides a ground for the internal circuitry.

Yea the mount tab is the 3rd connection.

Just an FYI …
The OEM 2-pin flasher works on the current draw of the incandescent bulbs.  It is a simple device that uses a bi-metallic strip (two pieces of different metals laminated together) that bends when heated (by the current draw of the incandescent bulb) until it breaks contact that sends the current to the bulb, turning the bulb ‘off’.  The strip then cools down (as there is longer a current draw) and make contact again causing the light to turn ‘on’.  This happens rapidly and the lights turn on and off.  
The problem with this flasher is that LEDs draw so much less current than an incandescent bulb that the bi-metallic strip doesn’t heat up enough to operate properly.
The 3-pin flasher is actually an electronic mini-circuit that requires a separate power source to energize this circuit when the turn signals are turned on.