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Old 05-30-2014, 12:38 PM   #1
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Default NA alternator swap issues

Recently I put an NA alternator in my NB MSM due to my MS2 freaking out about controlling the alternator and spiking voltage and I was tired of dealing with an ecu controlled alternator. I followed Jeremy at FM's instructions on putting it on my MSM

These are the instructions I followed :

Start by disconnecting your battery so you don't short something out. You also might 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.






My harness was exactly the same as the NA alternator, the gray and red was where the green and white was. I supplied the 12v switched from the ignition switch because I had previously had a wire hooked up to it (checked all my continuity and resistance of the wires in the alternator circuit to ensure it was fine)

Problem is, the gray and red doesn't charge the alternator (I'll see 12ish volts) but it makes the relays freak out clicking. I swapped it to the gray wire, and it charges the alternator (ill see 13-14.9), but my fan relays and AC relay do not work. I verified it was getting the 12v switched with both wires. It's odd how the alternator seems backwards, but even more odd the way the relays are acting. It's extremely odd that it even effects the relays as the alternator is on its OWN circuit now.

Anybody have any input? I'm pulling my hair out over this.
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Old 05-30-2014, 12:47 PM   #2
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Have the alternator tested for free at any auto parts store. Rule that out first.

It's interesting that they suggest you cutting up the factory harness. If it were my 10 year old Miata (pretty new compared to the original 25 year old cars), I'd be running new wires from the alternator to a 12v source under the hood, keeping everything else intact.
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Old 05-30-2014, 01:36 PM   #3
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When I purchased the alternator I had it bench tested before I left the store. I could have since I bought an extra pigtail from the junkyard, but decided to splice at the ECU harness anyways.
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Old 06-03-2014, 12:18 PM   #4
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Problem fixed. Apparently if the battery warning light is burnt out or not connected the alternator does not charge. Easily can diagnose for future people having similar issues by just checking the voltage in both of the wires coming to the alternator. Both are hot wires, I didn't realize it until I looked at the wiring diagram and saw that both wires came from hot sources.
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Old 06-03-2014, 12:27 PM   #5
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Props given for solution
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Old 06-04-2014, 05:31 AM   #6
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Quote:
Originally Posted by curly View Post
Have the alternator tested for free at any auto parts store. Rule that out first.

It's interesting that they suggest you cutting up the factory harness. If it were my 10 year old Miata (pretty new compared to the original 25 year old cars), I'd be running new wires from the alternator to a 12v source under the hood, keeping everything else intact.
What do you mean by this?

I am about to swap to an NA alternator due to the Haltech being ***** at controlling voltage and screwing with the tune.
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Old 06-04-2014, 10:18 AM   #7
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He's just saying he would touch as little of the factory harness as possible. In this case, it's a really straightforward swap with really minimal and easily-reversible wiring, so i wouldn't worry about it.
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Old 06-04-2014, 10:50 AM   #8
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Essentially you could use another harness pigtail and extend the green/white wire to switched 12v of your choice, and the other wire to your gauge cluster battery light. But, it would be a pain in the *** to run a new wire to your gauge cluster without touching the factory harness.

I bought one thinking the ends would be different and ended up not needing it. If you want it pm me, but I would recommend just splicing.
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