Bad alternater or what

Not sure what is wrong

We have a 2002 ford ranger. The truck lost power this past week as if the alternator does when it goes out. The battery died and we changed the alternator. There was very low voltage charge reading on the control panel?.the battery checked good. We change the alternator again but still have the same problem? Any suggestions?

Verify the interior gague reading at the battery,with a good battery and a alternator that passes a bench test,either something changes when the alternator is installed or you have a wiring problem (in paticular a ground problem) you may want to reasearch what part the PCM,ECM or what ever Ford calls it plays in the charging circuit.


The alternator has to receive 10+ volts from the battery, or, it won’t charge.
Check this link for the charging system wiring: On that page, under the header Charging System (2002), Ford Ranger 2000-2005, click on Charging System 2002.
Disconnect the wires from the alternator. Turn ignition key to RUN. Check the voltage on the light green/red wire. It should have voltage. I don’t know how much because it goes through the charge indicator lamp and resistor.
Check the voltage on the other two wires. Their voltage should be the same as the battery voltage (about 12 1/2 volts). If not, something has resistance between the battery and the alternator.