Even when I had my stock alternator on my 300e it was enough to power everything plus a 600 watt rms amplifier. I upgraded to the 150a because at idle my lights would dim and I swear my idle would hiccup. The sudden draw was too much for the little alternator at idle.

At speed everything was fine. Bottom line is that something is wrong, either it's not charging or maybe something is drawing too much power when you switch it on; like a short, but not enough to blow the fuse.

Electrical problems suck.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2