what year vehicle?

all MB alts have a trickle voltage (field) feed, and current feed.
key on, measure voltage to small wire, to case of alternator, and large wire (wires) to case on alternator.
report results.
did you have them test the replacement alternator in the store? I've had several bad in the box...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!