For several month's I have had the deal where at high rpm's the battery light flickers on. Yesterday, got in the truck to come home from work and the battery light was solid on. Figured the alternator was finally done so I took it out and headed to the parts store this morning (napa). Got a reconditioned one for about 140. Put it on, reconnected the battery ( which had been on the charger overnight. Fired it up and voila, the light was still on. Argh, maybe should have tested more first but I knew the alternator needed done so oh well. Tested the battery voltage with engine off, 12.68. Tested with truck idling across battery, 14.60. So it is charging, eh?

Now the battery in the truck (1999 4x4 4.6) is original so my next thought is maybe battery. Took it out and trip to Napa and they showed it had normal voltage but about 300 CCA. Since the battery is 8 years old, I got anew one for $75 and home to throw it on. Truck does start more crisply ( not as draggy) but alas, still a battery light. Found the Alternator Field fuse in my owners manual, 20 amp, it is fine. Disconnected the battery again for 30 minutes, reconnected and still on.

Ideas?? I know some don't like the NAPA alternator but the light was on before so I believe I changed a worn needy part but not the culprit.

Thanks guys.

 

Does anyone have any idea with the OP's problem? I have the same problem with my 98' F150 with 4.6.

 

are there any other things going on weird? If it works fine and the light is on why bother?

I would check the positive alternator wire, clean battery terminals, check the block-chassis ground wire block-battery ground etc.

 

The main thing I have noticed is that the head lights get dimmer and brighter (kind of pulses). You notice it at night and you can kind of hear the engine does the same thing, it doesn't stall but you can hear the way it revs kind of increases and decreases at the same rate the lights brighten and dim.

The check engine light does come on from time to time but I was told that was a sensor for the EGR valve was most likely the cause of it from the code it threw so I don't think it is associated with the charging light.

The reason I care is that the light is annoying and I don't want to be stranded somewhere because there might be another problem. I won't be able to check any of it right now as I broke my L1 vertebre Oct. 15 but I am hoping to have an idea what to look for this spring when I am allowed to work on things again. This truck is the truck I generally choose to drive but I have an 06' F-250 diesel I can drive if I can't drive the 150. The diesel has crappy tires and I don't want to replace them with 11000 miles so I just don't drive it much during winter and spring if I need to go off the paved road.

 

possible the rectifier/ voltage regulator has gone bad

 

Check the field wire to the alternator, it is the little wire that connects to the alternator. With 14.6vdc at idle with a new battery it sounds like the alt is runner at full output all the time.