New alternator, but the battery light is still on.

[silcom]

Explorer died on my wife, battery dead. I had the alternator checked and it was defective (130K miles). Bought remanufactured alternator and installed. Battery light remained on. Checked voltage, 14.5V, with alternator turning. Checked connections, engine off: B+ 12v, A 12v, all connections to battery junction also ohmed OK (I'm an electrician so have a fair amount of experience with meters). All fuses OK. Since cables to J box checked out, the fuse links are also good. Also tested 2 yr old battery, OK

Took alternator back and got another, still got the red light problem. Still charging just fine, the computer just doesn't know it.

Reset OBD, but those codes seem related to emissions. I commited the sin of shorting out the B+ when disconnecting the alternator, but the fuse links are still OK.

Any suggestions?

 

[Sams01XplrSprt]

welcome silcom

 

[BrooklynBay]

Welcome to this forum! I've moved your thread into the stock 2002-2005 section. Do you have a schematic diagram of the charging circuit? Trace each connection from one point to another. You might have a broken wire or a bad connection. It's also possible for the replacement alternator to have a defective voltage regulator or diode.

 

[jakedrew]

make sure all plugs are are connected tight?

 

[silcom]

Everything appears OK. But I'm not sure where the conducter from the alternator plug, I terminal I think, ends up. it goes to the computer that "talks" to the battery light, where ever that is. I could check the wire but just have basic prints out of a Haynes manual.

 

[silcom]

Alternator problem solved

This may help others after replacing an alternator.

As it turns out all connections, cables, and computer were in good shape. The problem was the two remanufactured alternators I installed simply would not communicate with Ford's "powertrain control module". They absolutely were charging the battery (14.5 volts and as much as 60 amps of current, just after cranking), the warning light just didn't know it. Further, the alternators were correct for my year and engine, according to the parts store. Went to the junk yard and bought a factory alternator out of a wrecked Explorer and warning light went out immediately.

Another problem was the parts store (large national) could only test the output of an alternator, they could not check the indicator circuit. Both their alternators checked OK. Also got bad advice from two dealers. One told me to drive it for a few days and it would "average" and reset, the other, for an hour labor, they could reset it. Week later still had the red light and figured a junk yard dog was a cheaper test than the labor.

Lesson I learned: when it comes to electric components, buy factory.

 

[BrooklynBay]

Thanks for the update!

 

[wbesack]

Hi, new member here. Wanted to say thanks for your thread sending me on the right path.

I had an alternator go bad, slowly, then finally quit. Replaced it with a reman from NAPA and the battery light stayed on and battery drained. Replaced the battery because it was very old and still the light stayed on.

I checked all the ground points, cables, continuity, and everything obvious. No error codes were logged. In the interest of time and nightmares about chasing an elusive short or control module issue, I took it to my regular shop. They scratched their heads a bit too for a while.

Issue ended up being a faulty alternator. I never believed so many would fail right out of the box but it seems to be common. The alternator had a computer printout stuck right on it showing the specific readings and results of the unit from the factory and everything passed. My mechanic said it would probably STILL pass a bench test. The issue it was having was only with how it interacted with the PCM. It could only be diagnosed on the car and by checking specific voltage points.

Got stuck paying them $40 for the diagnosis and $65 to turn 3 bolts but the light is out. Thankfully NAPA delivered the replacement to the shop free of charge. All is well. I don't really blame NAPA or any other reman vendor - they did their due diligence in testing it from the factory, but maybe as a rule they should be replacing the electronics along with the obvious things like bearings. I got what I paid for...which in the end, didn't really save me much.