I did this on my 855.

Pull up the floor where the spare tire is and, on the left side, there is module that distributes power to all of the rear lights.

Without cutting any wires, I was able to tap into various conductors in that module and come up with all of the signals necessary to get parking lights, turn signals and brake lights, without triggering the dash warning light.

The scheme required me to use two power diodes from Radio Shack, but it's been in-place for about 10 years with no problems.

If you can wait until this weekend, I'll pop the floor and take some photos.