Replaced Alternator and Battery - Still Not Charging

H/C/I Stang

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2003 MSP
I recently picked up a MSP with the battery light on. I was told that there was some "cable" that wasn't connected during the engine build.

Well, the alternator is not charging (tested with a DVOM @ 12.3V with all accessories on at idle.)

The car died 2-5 times while driving at a very low speed (less than 5mph) with all the accessories on and turning (forcing the power steering to work.) Sometimes, the car wouldn't start if the accessories were on. It would click as if the battery was dead. I've had to push start it the past two starts after sitting for an extended period of time.

I checked any and all fuses - Good

I checked the alternator power wire and connections - Good

Replaced the battery with a new one today.

Replaced the alternator with a new/reman'd one today.

Alas, still no charge at idle (12.0-12.3V with all the accessories on.) It shows 13.05-13.1 at idle with only the headlights on (HIDs.)

What would be causing the light to remain on and still have no charge? I haven't climbed into/under the bay to check for loose wires, but I'm hoping it will be a simple fix. Anyone have any similar issue(s)?
 
whered did you get the reman'd alt from? i did this...had to replace my less than a day old reman'd alt with another new reman'd alt. so far its been fine. but the new one i had to replace was only doing 12.25. took it back the next day and it failed the test bench instantly.
 
thats where i bought mine. i bet if you take it back out and have the test it its probably bad. i was told i would probably have to replace it three or four more times til i got a GOOD reman'd one. luckily it took two and ive been good so far.
 
I'll pull it out and have them test it.

Maybe get them to order five and check them all before I install any more of theirs...

Thanks for the hope.
 
no problem man. trust me i was super pissed that the damn thing didnt even make it a whole day. then i had to drive across town to pick up the closest replacement. i spent like 3 days just working on the damn alt.
 
Went back up to Autozone and had them test the alternator while it was on the car.

Same readings I noted when I checked it at my house.

I pulled the old alternator out of the box and had them bench test it. It passed their machine. Yet, only yesterday, it failed the in car load test. Granted, the in car test was tested at idle and it seemed the bench test was performed at a much higher RPM.

The man that helped me told me to pull the alternator out they sold me and he would refund my money.

I take the "new" alternator out, clean the old one (externally with electronics cleaner), sand down the negative battery ground (to transmission) and battery cable terminals.

I started the car and the battery light was still on.

I then tested the voltage at idle and recorded a steady 12.71 with the accessories on. I then retested the voltage with the RPMs raised to 2,000, as suggested by certain manufacturers, and recorded a reading of 13.41.

So, the alternator seems to be charging the battery sufficiently at speed, but not at idle. That problem SEEMS to have been solved.

Still, the battery light problem evades me. Anyone have any insight on that demon?
 
You'll get thebattery light because the alt. Is charging... But it should be up at 14-14.5 at idle from the alt. Same problem I had. My new alt was doing the 12 or so at idle and I had the battery light. Switched to the 2nd new alt. And my battery light went away because it is now getting the proper 14 volts. I still recommend you get another new one. The batt light is telling you that it's not getting the proper charge. It will ruin your battery.
 
I agree. I think the whole, 13.4v at speed is garbage.

It should be receiving more than that at idle, like every other car.

I'll go back tomorrow and have a new one put on order.
 
An unplugged MAF or IAT sensor will also turn the battery light on. Make sure those things are plugged in...
 
Agreed...the battery and alternator are not the only things that can make the batt light stay on. Broken wire at my iat sensor and frayed wire to my cam position sensor in two different instances caused very rough idle and batt and cel light to come on.

You need to get the cel code read to really know whats going on!

An unplugged MAF or IAT sensor will also turn the battery light on. Make sure those things are plugged in...
 
An unplugged MAF or IAT sensor will also turn the battery light on. Make sure those things are plugged in...

Are the IAT sensor wires blue and orange?

If so, they're not plugged in and have nowhere to be plugged in. I have a FMIC and it looks like there was never a bung to have one installed.

Next step?
 
Are the IAT sensor wires blue and orange?

If so, they're not plugged in and have nowhere to be plugged in. I have a FMIC and it looks like there was never a bung to have one installed.

Next step?

the IAT being unplugged will not cause a batt light, however bad wires to the IAT will.
 
the IAT being unplugged will not cause a batt light, however bad wires to the IAT will.

They're both shorts in the circuit.

How could one be different from the other...?


Should I pick up a new IAT sensor or is there a way to fool it (resistor method?)

EDIT: I will NOT be buying a new one seeing as they're $210...

DOUBLE EDIT: I was looking at the IACV for some reason =\
 
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The sensor not plugged into the harness is an open circiut just the same car-parts.com or maz-max.com will have one cheap.
 
Another thing to look at would be where the voltage regulator is at. For example, in the older Miata's the voltage regulator was in the alternator, but when they switched to the '99+ Miata, they put the voltage regulator into the ECU. The voltage regulator is what tells the alternator how much to charge, and when. If the regulator is bad, it might charge at speed, but not at idle, or the opposite as well. Good luck. I will say that you really need to get all the other issues taken care of first, before you try to track down an electrical issue. No sense chasing multiple problems all at once. Take the alternator to another place, like advance auto and have them test it.
 
Autozone remanufactured parts are grabage. It is just a ploy to get your money every time you come back with a failed alternator. If someone brings me any parts from autozone I just tell them to take it back and get one from NAPA, Advance Auto, or o'Reilley. Remanufactured alternators are usually crappy. New is best. They only rebuild the failed part and the rest is just cleaned and or painted.
 
Also check for corrosion on the battery terminals and the posative cable running to the generator. Very easy to overlook...

P.S. I see you are in seabrook... Man I hate Seabrook PD!!!
 
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