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2001 F150 with 4.6L. The battery light keeps coming on.

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2001 F150 with 4.6L. The battery light keeps coming on. It flickers and sometimes will just stay on. The battery tested bad so I put a new one in. The alternator was removed and tested at two different locations. It tested good (15 volts). I replaced the battery ground cable due to heavy corrosion. Check all connections for security. The light still flickers. Need help. Could the alternator/voltage regulator be going bad even if it tests ok? HELP!
Hello.I am Randall. Do you notice at anytime any trcks lights flickering etc or just charge light?

has truck always cranked and started and run ok?
Customer: replied 5 years ago.
Lights don't dim or fade. No problems starting and it runs great.
How often is the light either flickering or staying on? one time or so per day or every couple minutes, much quicker or just sometimes?
Customer: replied 5 years ago.
It started last week. It comes on occasionally but when it does it flickers for awhile (few minutes) and then will just go out or stay on till ignition is turned off. Sometimes it will reappear on start-up and other times it won't. Very unpredictable.
Thnaks, sorry for all the questions,. I need to pull up some info and diagrams. Then get back to you. Let me do this and get back with you shortly.
Customer: replied 5 years ago.
There is no way for me to know how it was tested as every tester is different but 15 volts is a bit odd as the regulated charge volts should only be from 13.5-14.8 volts. In any case it sounds like they passed the alternator both times

The problem I have is.. it will pass each time UNLESS you take it in and they run it on tester long enought till the problem happens. You said its unpredictable. Each time you have taken in it may have been just fine. having light come on, remove alt, get to tester? yes.. it very well will test ok each time. Intermittants are very hard to find sometimes

The thing to do is do your own testing. get a cheap Volt meter for 12 volts and the next time light comes on, touch the battery terminals with the leads and you should see around 14.8 volts. If out of this range,, then you most likely have an alternator failing or more so the internal regulator.

It is very rare for the cluster or wiring on a vehicle this new to cause the problem but cant rule out. You must catch it in the act with meter on the battery terminals. You either have around 14.8 volts or do not. IF light is on and you test and it IS around 14.8 volts, then you have a problem within the instrument cluster most likely

I am leaning to bad alternator. Just recheck all connections to really be sure. be sure all clean and tight

here is a symptom chart and you will see on left column the symptoms and right column the possible causes.


Randall C, ASE MasterTechnician
Category: Ford
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Experience: 35 years ASE Master Tech, Diagnostic , Electrical Specialist
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Randall C , ASE MasterTechnician
Category: Ford
Satisfied Customers: 12661
Experience:  35 years ASE Master Tech, Diagnostic , Electrical Specialist
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