Hmm.. If you want running lights and brake lights, the rear brake switch is not the place to splice in. For that functionality, you'll actually want to splice in at the brake light. The brake light bulb has two filaments in it to support this functionality, and the brake light harness will have three connections (as discussed below). If the wixom wiring harness only has two connections, then you won't be able to have both running and brake lights.
That said, at the brake light you'll have three wires, (I don't know the colors), one will be "running light positive", one will be "brake light positive", and the third will be "ground". Some wiring diagrams have this information, or you can determine it with a voltmeter.
