How to diagnose and fix dead battery Ford Focus
If you have a dead battery Ford Focus condition, a system that’s not charging, a battery light that stay on even after replacing the alternator and battery, read this. This problem can really throw a pro for a loop because the problem may be a bad wire or a corroded fuse.
First thing to check is a broken or intermittent wiring connection at the alternator. The “FIELD” charging current is provided to the alternator by the PCM on the blue wire. Sometimes this wire can break, making it look as though the alternator is dead. So check continuity on the blue wire from the alternator back to the PCM. If it’s good, move on to the red wire. The red wire pumps power out of the alternator and back to the battery.
There’s a 175-amp fuse in that circuit and it sits at the front of the engine—right in the worst possible place for corrosion. If the connections corrode at the fuse, that alternator can pump its guts out but the power will never reach the battery. First, check the red wire for continuity between the B+ post on the alternator and the red wire coming out of the fuse. If you get continuity, check for voltage drop across the fuse. Some owners are finding severe corrosion on this inline fuse. If so, correct the problem and you should be back in business.
© 2012 Rick Muscoplat