This alternator service/swap 150a to 90a was done as and experiment since I decided I didn’t needed the big bad 150a for my needs and could possibly achieve some very small MPG gains w a 90a. Now 3 years later I can say there’s no noticeable difference...
FYI the alternator on my 4-cyl AHU TDI engine is the same as the ones on the VR6 engines and IIRC the 93-95 5-cyl models as well. The two are a direct swap physically. Later 2001-2003 models might have a different two pin plug style (oval vs. square) but this is something easily remedied by sourcing the correct plug (ubiquitous and STD on a basically all VW models (Jetta, Passat, Golf, Etc) in a variety of places on the wiring harness pre 2000) and replacing yours with that—slickly by re-pinning but functionally the same via shadetree methods by cutting the OE plug and installing the correct one to match the alt via your preferred method, soldering or quick butt to butt wire coupler.
150a alternator on the top, 90a on the bottom
Brushes still functional with normal wear but down to the last 25%
New brush pack on the L. Brushes still functional with normal wear. The Bentley wear limit is 0.10mm iirc so technically within limits but as they say, “an ounce of prevention is worth a pound of cure…”
New brushes installed
Part number for reference
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