I just tapped into the green wire (I did the same thing on the e46, e39, e60, e63, e82, and e92).... the hardest install yet was the m6...
here is a pic of what I had our m6 looking like mid install... there was no place to ground the thing b/c it was a cab, so I had to run it down the windshield channel and use the sun-visor mounts...
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16 M2 & 03 M5 - current
95 540i- sold, 09 135i - sold, 08 335i - sold, 07 335i - sold, 10 550i - sold, 99 m3 - sold, 06 m3 - sold (regret).
01 325ci - sold/gone/my 1st car, (later found abandoned in a field w/ fire damage).