Another thing to keep in mind just because you have a 100 amp alternator doesnt mean its charging the battery anywhere close to that. The alternator varies based on load. Any serious amperage its making is to feed the cars accessory needs or changing the battery back right after cranking. Most of the time there isnt much of a charge going into the battery itself.

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Just BMW's - All cars and trucks was two pages long
1994 318is
1997 528i
2000 323i
2001 X5 3.0 auto
2005 X5 3.0 auto
2011 535xi auto
2013 X5 xdrive35 Turbo
More are at my website

Aftermarket E53 Radio Install