I'm working on a 2007 Escape 3.0l with 278k miles. The battery light comes on intermittently. I replaced the battery. Same issue. Took the alternator off, had it tested. First test was bad. Bought new alternator, installed it. Immediately charged 17.5 volts. Returned the alternator, had it tested. Tested good. Asked to have the old alternator tested again. It tested good. Installed the old alternator and everything was fine for several hours. Eventually, the battery light came back on again. Shut the car off for a minute or two, restarted it and everything was fine for a little while. Same thing, battery light comes on, shut it off, restart, fine for a while. I tested all the wires to and from the alternator, all test good, even when battery light is on. I don't have access to an oscilloscope or to a multimeter with duty setting. I was hoping that someone has ran into the same thing and found out exactly what it is. I don't want to just throw parts at it. Thank you for your time and consideration in this matter.

 

What are the resting and running voltages of the battery when the light is on?

 

The voltage was around 11 volts. I went to Harbor Freight and bought a multimeter with duty setting. Found out the computer wasn't putting out signal to the alternator. The voltage going into the computer was 12 volts but the voltage coming out was 8 volts. After testing the duty and voltage found out the computer was bad.