How to install a cheap 90A alternator
 

Couple of weeks ago I changed my stock NA8 alternator for a 90A alternator off a Milenia. Overall I'm very happy with the change. My voltage in boost is higher and very stable, it bolts in fairly simply and only weighs 2lbs more than my NA8 alternator.

I paid $20 at a junkyard for a mint, clearly replaced, Millenia alternator. There were so many eligible cars at the yard, that I just picked the nicest one.

Here's a how to.

Where do I get a 90A alternator?
In United States, virtually any FWD Mazda or Ford equipped with the Mazda V6 'KL' motor had a 90A alternator. That means some 626, all Millenias, MX-6, MX-3, Ford Probe V6, etc.

What are the differences between 90A alternators?
Mazda 626 have a 2-pin connector, identical to NA connectors.
Millenias have a 3-pin connector, unique connector.
Internally they are all same, internally regulated, 90A alternator. Just find the one that looks best.

What do I need?
Grab the alternator and the pigtail, just in case.

How easys is it to remove?
Surprisingly hard. The V6s use a serpentine belt and are transverse moutned. The alternator is at the front of the car, but there is very little space to remove the bolts. Bring wrenches and shallow sockets. The alternator is solid mounted to the engine, so at least thats easy. Basically, its a bit knuckle busting.

How do I mount it?
Same as miata with some minor differences.
- The bottom bolt is reversed. Instead of inserting it from the back, it goes from the front. The reason is that the bottom holes are are threaded in the opposite way. Once you see it, you will figure it out.
- The top lug is offset and thicker, making it impossible to use the NA tensioner. You can use the stock bracket, but it needs to be offset a little bit to be parallel. Since you cannot use the tensioner, you need to put leverage on the alternator to tighten the belt as you tighten down the bolts.
(or you can use a heim-style tensioning rod)

How do I wire it?
The power cable is same M8 nut as NA8 cars (and probably NB). For NA wiring harness you will need to either install a new, bigger, lug or enlarge the lug on the stock wire.

The other connector is either 3 or 2 pin, depending on donor car. They are color code same as miata wires, though (at least in my case)

For 2 wire:
1) +12V sense - this one is just always-on, fused 12V (white-green)
2) Dashboard light (white-black)

For 3 wire, same as above PLUS
3) +12 switched - this one is off when car is off, and on when its running.

That's it.

Nice write up. Good info here. I found most of this out when attempting to use the millennia alternator on my KL. ended up not using it and throwing it into the scrap metal bin but would be a nice swap for the BP. Good to see it is actually simple to make it work!

Anyone know of a straight swap-in alternator for an NA6? There are never any Miatas in my local yards, but plenty of older Proteges, 323s. I know I can get an NA8 one in there with some work, but I'd rather not if I don't have to.

I've got a na6 alternator I'll sell you for cheap. pm'd.