How to: NB to NA alternator swap
 

So my alternator took a dump on me and honestly im glad because I used the oppertunity to swap in an NA altnernator. Why do this you ask? Because the NB alternators are controlled through the ecu for voltage control. When you switch to an aftermarket stand alone ecu, this is a parameter that you have to tune and its a needless pain in the ass. NA alternators have a built in voltage control so by switching to one, you wont have to dick with it anymore. Itd does everything for you.

Jeremy at Flyin Miata gave me the directions and all I did was just change it a little so its a tad easier to understand. Mind you this is for an MSM!




Start by disconnecting your battery so you don't short something out. You'll also need the harness pigtail for the 94-97 alternator.



- The big white wire is the same for both units.

- There's a 2 wire plug in the 04 alternator with a grey wire, and a grey / red wire. Cut off the 04 plug, and splice the grey wire into the white / black wire of the 94-97 pigtail. Next splice the grey / red wire into the white / green wire of the early pigtail. Plug it in to the alternator when finished..



We have to move these wires, but we'll do it at the ECU plug (under the dash, by the steering column) where they're easier to get to.

-The grey / red wire goes to 3M at the factory ECU plug. Cut it off, and splice the harness side of the wire into a switched 12V source from the main relay.

http://i94.photobucket.com/albums/l1...yparty2009.jpg

-The grey wire goes to 4T at the factory ECU plug. Cut it off. Also cut off 3U (brown / red). Splice together the harness ends of 4T & 3U. The ecu will no longer be controlling anything with the alternator and you should now be seeing 13V continuous.

http://i94.photobucket.com/albums/l1...rty2009001.jpg

In the Hydra you don't really have to do anything. I turned the alt control off though just for the hell of it.

Have you logged voltage since the swap?

I need to do the same thing on my 99, does anyone know if the wiring at the ecu is the same?
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote

Very nice informative thread.

If anyone is not in a rush, I'll be developing a digital circuit to control the NB alternator. The code to do it is ready and tested, I just want to do it properly with a PCB rather than on a Veroboard.

still applies... I think some of the stuff has a different name on the ecu pinout, etc. basically what i did was open up the 94 wiring diagrams... and the 99 and make mine match the 94 for the charging system. Basically you are just bypassing the ECU and making direct connection between the alternator and battery. I had a pic... but I don't think I have it anymore.

Phil did you ever figure it out lastnight

did all this right off the back of the ECU

1T (gray) goes to 1Q (brown/red)... bypassing the ECU

Then 1O (gray/red) I just ran right there off a switched 12 volt source off the fuse box.. again bypassing the ecu so its a direct connection to alternator.

Attachment 193188

I know this is an old post but thank you aaronc7 for the diagram. Converted car back to stock for smog and never knew you had to do this since I was running MS3x when I did the NA alt swap. Did everything from the dash in about an hour. Worked perfect on my 01.

Some-what related to this thread. When doing this conversion, can we bridge the L wire (that goes to the bulb) to the switched 12v wire instead as this would prevent having to run a wire to the dash to the alternator light. What resistor side is required, would a 470Ohm, 3watts be sufficient?

EDIT: Turns out the reman alternator was just trash. It slowly died over the couple weeks that I had it. I'm guessing the circuitry in it was FUBARED and was letting voltage leak through it unless it had the always on 12v. I replaced with a "new" reman alternator and went back to the switched 12v and there is no voltage leak.



--------------------------
Bumping this because of an issue that I had to track down after doing this swap and hoping to save some people a headache. When I had the gray/red going to switched 12v my battery was dying in about 1.5 days of not driving. I used a multimeter to measure amperage between the negative battery post and the terminal connector. Trial and error got me to the alternator. If i disconnected the alternator's main power wire the current would be gone. If I kept it plugged in and disconnected the alternator harness the amps would read the expected 0.03 to 0.04 amps. I changed the harness wire from switched 12v to constant 12 volt and now there is only about 0.035 amps with key off.

For those of us with Megasquirt and a full aftermarket dash, obviously the charge indicator wire is not needed.

Is the 12v switched wire required? Or can I just run an NA alternator with solely the white charge wire connected?

The internal regulator needs to monitor voltage to….regulate voltage. I’ve seen a lot of race alternators jump this 12v to the battery post of the alternator if you want to try that.

That's exactly what I was wondering. In my case, for an Exocet, my amperage draw is fairly low and I'm pretty confident in consistent voltages throughout the [minimal] systems I have running.

MSM with NA alt
 

I have done this wiring change in my MSM and it has been running good for about a year now. I agree with the reasoning for the swap; less to dick with in the ECU.

I don't entirely blame you, however this thread was created 12 years ago, alternator control hasn't been an issue with decent ECUs for at least half that time.

I did this on my NB1 in order to run a RX7 alternator on my car. That was over 8 years ago and I haven't had a hiccup.

Can confirm this on my nb as well had the same problem 0.5 amp draw, switched it to battery constant 12v and now the draw is 0.01 amp