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Old 04-08-2010, 12:10 PM   #1
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Default 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 ***. 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.



-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.



In the Hydra you don't really have to do anything. I turned the alt control off though just for the hell of it.
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Old 04-08-2010, 01:51 PM   #2
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Have you logged voltage since the swap?
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Old 10-29-2010, 07:56 PM   #3
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I need to do the same thing on my 99, does anyone know if the wiring at the ecu is the same?
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Old 10-29-2010, 10:34 PM   #4
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Very nice informative thread.
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Old 10-30-2010, 05:02 AM   #5
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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.
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Old 10-30-2010, 12:44 PM   #6
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Quote:
Originally Posted by levnubhin View Post
I need to do the same thing on my 99, does anyone know if the wiring at the ecu is the same?
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.
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Old 10-30-2010, 12:48 PM   #7
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Phil did you ever figure it out lastnight
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Old 10-30-2010, 12:57 PM   #8
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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.

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