Okay guys, I've got an 04 MSM, recently replaced the alternator. Car runs a Rev Built MS3

The alternator (original) was making a horrendous noise every now and again, and when the noise came about, it wouldn't charge. So most likely worn bearings.

Bought a remanned unit from O'Reilly's. Put it in, and it's charging. Cool.

My wife has been driving the miata (for a few weeks), and she neglected to tell me at night, when all the accessories are on, and if she hits the brakes the battery light comes on.

I drove the car, and confirmed it.

So today, I checked out the usual stuff, grounds (PPE, DIFF, Chassis, throttle body), and all of those check out good.

If I leave the fogs off, but head lights (HID kit), A/C on, voltage drops to about 13 or so. Tap on the brakes, and it drops to 12.4 or so.

Battery is old, I don't know if the PO ever changed it or not, but do y'all think it's more along the lines of a shitty battery or alternator?

 

Get the battery tested and then take the alternator to a rebuild shop and have them test it. Could be one of the copper coils need to be resoldered.

 

I know @curly has had some ridiculously shitty luck with rebuilt units. OEM or bust he says.

 

Congrats, your reman alternators works some! Those things typically fail a lot worse than what you're describing.

Solution is get a better alternator, it can't keep up with the electrical load your car has.

 

that's not a battery issue.

id take it back to get tested. i always have to go through 2-3 re-manufactured alternators or starters.

 

Well I put a new battery in it anyway, since the old one was leaking a bit, the part numbers from O'Reilly's is actually "MIATA". Weird lol.

It's a bit better, battery voltage doesn't drop down to the 12's very long when there's load. So I dunno. Unfortunately, my wife is car-less at the moment, so she's stuck with the miata.

 

the NB alt with controller should almost always just be dead on at 14.5v or so.

 

Bad alternator.

 

I had 3 bad reman alternators from vatozone in a row. I found a local place that rebuilds them and had much better luck with that one.

 

Ping Reverant about a small mod to improve the collaboration with reman units.

Remember that the Battery light is a multi-function warning light with a Rev Built MS unit, not some simple stuff directly related to the Alternator.

I have a rebuilt Alt that works fins with the Stock ECU but gives me noting on a default MS3 Basic. I have an email with Rev's suggestion somewhere (never tried it, simple to switch Alt instead), but you're better off getting the latest & greatest suggestion for your unit from the horses mouth.

A cheap digital panel Volt meter have saved my bacon several times. Just connect to the radio/lighter power and you will always know how the battery/alternator are doing.