In case this is not obvious, if your idle voltage is 12.5-12.8v, it is not charging, which means it is discharging if you have a lot of accessories running, to the point a run down battery if you idle it long enough with the blower and headlights on and your 1000W stereo thumping away.

I think if you put a smaller pulley on your 65A alternator, it may push it over the threashhold where it will charge at idle. Has anyone tried that? I think my 120A alternator has a smaller pulley diameter than the 65A unit it replaced.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked