Yes ANOTHER Alternator not charging
 

1999 Miata with Hydra ( pausing for hecklers ) working fine for years and then the motor blows. Motor pulled, rebuilt, motor put in the car along with new reman. alternator. Car has starter trouble which turned into quite a nightmare by itself as the Advance Auto starter would just make a horrible grinding noise against what I assume was the flywheel. Put on a buddies old starter and car turns over slow. Small battery is old, replace battery with PC925 and buy new OEM starter (reman for a ridiculous price). Car turns over well but not charging. Bad judgment ensues and I put in a used 94 alternator without changing any wiring and get mid 15ish volts which troubles me as anything past 14.8 shuts down the heater in the wide band (they say). Pull that alternator and put in a working 99 alternator and no charging. The odd thing is that there's no light coming on in the dash either. Open up laptop and get into the Hydra and change values of Alternator Target settings as well as changing "P" and "I" values to which NOTHING happens. I have a voltmeter gauge wired in to see real time and it does match a voltmeter reading at the battery. I check engine ground which seems to be fine. The ODD thing to me is that there's no light on in the dash and that the HYDRA always is lit on the first box of "Target Alternator Settings" under the temperature of -4 degrees F.

So you would assume it's a bad IAT except that the other parameters that read the IAT seem to have a correct value, certainly NOT at -4. Also the Hydra is showing a live voltage read which is NOT accurate but seems to be "live" as it oscillates up and down just a bit. This is normal as I'm told HYDRA never reads the value correctly for voltage and certainly mine never has. It can say there's 11 volts and the car at the battery will have 14.6. Meanwhile the target voltage might be set to 13.0 Volts. It's more like "Values" which you move up and down. If you want more volts, you plug in 13.2 and normally if it's working correctly it will raise the voltage to the battery to something higher than 14.6.

I've looked at the wiring change to bypass the ECU for an NA alternator and I've noticed that the one with the diagram said to cut the pigtail off the 94-97 alternator. I'm not understanding this as the 94 alternator I purchased (used) has exactly the same plug inlet as my 99 has. Can't I just reuse the same plug and cut Gry/RED wire and splice it into a switched 12V source and then go under the dash to splice the Gry wire to the Brn/RED? Can anyone verify or deny the plugs for the alternator are the same for NA as NB1?

Thanks,
Ken

Update: This evening I checked wire conductivity between the gray and gray and red wire at the alternator plug into the plug at the ECU. There is no short or break there. Tomorrow I'm going to run a jumper cable from the negative post of the battery to the alternator and try it one more time. If it still doesn't charge then I guess I'll cut the wires and reattach them for the 94 alternator and just run that for now. What a pain.

Where are you located? That might help. I have a little experience with hydra (2.6? 2.7?), and at least the 2.7 is a great ECU when installed and tuned by local expert Kris at KO Racing. The NB and NA pigtails are the same AFAIK, however the two wires do something completely different. NA is a 12v supply, NB is a 12v output I think, with the other wire on both being the alternator light, IIRC.

As for the charging light, chill, I think it only turns on with low voltage, not high.

I would be concerned that if you hooked up the NA alternator to the Hydra's output without rewiring properly you may have blown the output on the chip.

Do you have access to an oscilloscope? That's the right tool for debugging this.

--Ian

And so.....
 

Located in Keyser, WV, at least a 100 miles from no where. LOL. I dont have access to an oscilloscope sadly and to be honest I wouldn't know how to use or read it. I have an autocross tomorrow so I'm going to have to rewire for the NA. I will make it reversible and tidy all under the dash though, then I can go back and maybe figure something out.

The ground attachment didn't do anything. Matt from Flyin Miata said to check voltage on the alternator pins while the car was running so I did that under the dash probing the rear or the pin in the wiring harness plug and got nothing on either pin.

Thanks for the replies guys. This car I've renamed to Killjoy.