The Mercedes-Benz R129 series of roadsters share many parts with the W124 series of sedans, coupes and wagons. The R129 cars came with many more power accessories, however. Things like power seats, mirrors, tilt wheel and the power top all added electrical loads that were much higher than the regular
4-door sedans. That is why the R129 cars got not just a larger battery, but also a more powerful alternator.
Both alternators look virtually identical on the outside.
They have the same mounting points, the same drive pulley...
...they even have the same voltage regulator.
The major difference is in the back where they connect up to the cars’ wiring harness.
Here the difference is both important and obvious. The 80-amp model uses a black plastic plug, with three spade connectors inside.
The 100-amp version hooks up to a much larger pair of threaded lugs on the back. These enable much higher current flow and mate up to the thick ring terminals on the wiring harness.
Before ordering a new or rebuilt replacement alternator on any car, be sure to check the connector arrangement on the back to match the right one.