The only 80A replacement alternator requires a different wiring harness, not a exact bolt-on due to this! WAS this done?
If this isn't the case then you probably got another 70A alternator.
ORIGINAL alternator in Bosch reman is a AL65X(70A), the 80A is a AL66X & THAT REQUIRES 124-543-45-26 wiring harness.

Undercharging is a common problem on the 300E's upto 1990!

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