Last night battery light came on. Drove 40 miles home with lights on. Today, it started so I headed out. About 10 miles of battery light on, gauge fluctuating mildly either side of middle, gauge suddenly drops dramatically. I turn around and head back. After a mile or so there's a terrible growling under the hood, sounded like it could be an alternator bearing. Just as I pull over, the noise stops but entire dash goes black. Popped hood, alternator spinning quietly and not hot. I drove back and it started stumbling and surging as the battery died and it finally quit almost all the way back.

I have battery on charger now.

I assume the BCM is the regulator by feeding current back to the field? If so could the growling be the BCM feeding back a huge field and the rectifier bridge growing? And the BCM fuse blew because too much current to alternator field coils?

Will it start with a charged battery with the BCM dead? I need it to run to get to the parts place. Which fuses do I need to check? Then, how do I check the alternator, wiring, BCM regulator to find original problem?

Thanks,
Mark

 

What year and engine?

I would take a look at an electrical diagram checkout everything in the starting and charging circuits.

 

Sorry, 2006 F150 Extended cab, 4x4, 5.4, automatic.

 

Since then, I charged for 4.5 hours at 15amps, put it back in the truck, started right up, dash works again, back to only problem is the battery light and weak charging.

The BCM may or may not be the regulator for the alternator. I guess, on a guess, I'll replace the alternator.

Mark

 

The alternator is KAPUT!
You are going to destroy the battery by trying to run on the low alternator output.

 

Educate me please. What is a BCM? As you were, I figured it out. Battery Control Module, right?

 

He probably means PCM, and yes it is a PCM controlled charging system. The alternator can also overcharge and cause the instrument cluster to shut down from over volting. But in this case it is obvious it is under charging and the system shut down because of the lack of voltage to operate. I would test the battery after replacing the alternator, as a completely dead battery is hard to recover when they get that age.

Old Guy, the vehicle also has a BCM, body control module which controls things such as autolamps, vehicle security, door locks, etc but it has nothing to do with the charging system.

 

Thanks guys. As noted, the PCM controls the field current, not the BCM. The BCM (or whatever module controls the dash) must have just shut down for low voltage. Thank goodness the PCM didn't as early.

How do I verify the alternator? Remove field wire and jump to 12V?

Thanks again,
Mark