jorb,
I have wired it three ways:
1. As described by you and by the instructions
page 11 and
page 12 .
2. Ran/used the original white tail light wire to the white lead on the original tail/stop lamp, and the black brake lead to the black wire on the original lamp. These were quite dim, so I tried #2.
3. Ran the black brake lead to both wires (lighting both filaments) in the original lamp. These were quite dim, so I went back to #1.
Some day, I will put 6v dual "filament" LED bulbs in those lamps and see if they are brighter.
