After swapping pullys I noticed the nut did not sit all the way down on the GS alternator with the BP pully. In other words, the bolt or whatever that the pully attaches to did not protrude out of the nut, but rather was inside the nut by maybe 1/8 or 1/4 inch. While disturbing, this did not stop me.
The little bolt (or whatever you might call it) that the negative cable loop goes around was bigger on the GS version. So I had to bore out the little ring attached to the wire. I suppose if you were prepared you could just buy a bigger loop attacher thing and cut and splice.
As others have noted, the bottom mounting bolt (on which the alternator swivels) has to be longer (and threaded all the way) and enters from the other side of the alternator. I ended up ordering the offical Mazda MX-3 GS Alternator bolt from the dealer. Getting it in from the other side though, proved impossible. The frame of the car (or at least MY car) blocks the bolt from a straight entry into the hole. I ended up loosening the engine mount bolts on that side of the car. That allowed the engine to drop enough to get the bolt in straight.
Finally, the old top mounting bolt threaded into the alternator itself. The GS version needs a bolt long enough to go through all the way and a nut on the other end to hold it in place. I think I reused the bolt that came with the BPT which needs an M10-1.25 nut (how's that for precision).
The GS alternator is Fat so I had to remove the one side of the upper strut bar to get it in. Also ended up jacking up the car on that side to see under where the alternator bolt has to go in. This may not be necessary.
So I think that's about it. Definetly solved my electrical problems. If I left anything out, let me know. I'd be happy to answer any questions. This MX-3 is getting old and tired. I want a Mazdaspeed 3.
