Battery Should But Won't Recharge

1992 Ford Ranger 2WD/4cyl. Replaced alterantor with new one that tested good and replaced battery with a new one. System still won’t charge battery and the engine drains battery of all voltage. Seems temperture related. Guage on dash reads 14V and system charges when above 50 degree. Gauge reads about 10V when below 50 degrees and system won’t charge battery. Thank you. Please help!

The alternator is faulty or the wire that feeds alternator power to the battery is faulty. At 50 deg or less, something is failing. Wait until a cold day when the volt meter is low, like 10 or 11 volts. Use a multimeter, and check the voltage at the battery terminal of the alternator. If it reads under 13.5 volts, the alternator is faulty.

I just had a similar problem with my Merkur (a relatively unknown Ford product).
It was a real pain to diagnose, as the alternator was testing good when I took it off and had it checked, but would read bad when it was actually on the car.

I don’t know how much relevance it’ll have to your problem, but in my case, the little light bulb for the battery light in the dash had burned out- and the “exciter wire” for the alternator runs from that light bulb. Hence, with no current from that wire, the alt wouldn’t charge when the engine was below a certain rpm.

Like the others mentioned, you have a bad connection somewhere that is for sure. The trouble may be with the wire between the battery and the alternator. To see if that is so check the voltage between the alternator output lead and the positive battery post while the trouble is occuring and the engine is running. If the connection is good then you should see less than .1 volt across the lead. A bad connection will show a higher voltage due to the voltage across the bad resistive connection.

O.K. Thank you all!! I got a repair manual with wiring diag. Every wire tests good. Still won’t charge under 50 degrees. I have noticed that the “rear antilock brake” light comes on evey time the system won’t charge and it not lit up when the system is charging. I remove the RABS fuse and the situation remains the same. Does anyone know where the RABS modual is located on this truck? Manual is not clear as to it’s location. Perhaps I can unplg the wire on the modual to see if this is worth chasing. Please still help. Thanks in advance.

Did you check the voltage at the alternator output tab when it wasn’t charging?

I think the ABS module is responding to the low voltage rather than causing it. I think the alternator is failing at low temps. The only way I can think to test it is to take it in when the temp is really cold. Don’t let it warm up in the car with the heater on. Use the trunk. Make sure the case is cold when the hook it to the tester.

If you what to try the ABS module, it should be located under the hood. Just trace the brake lines from the master cylinder to the rear of the truck, and look for it.

Check the voltage going to the ‘L’ lead on the back of the alternator while the trouble is occuring and see if the voltage is close to the battery voltage. If it isn’t then there is a problem with that lead. The waring light usually ties to that lead and is in series. If there is a bad connection to the lamp then the alternator will not work.