2003 ford f150 battery light comes on and battey guage pegs at high output all lights that are on get really bright then all guages reset replaced alternator 6 mos. ago

Sounds like you may have a voltage regulator going bad in your alternator. They will usually check them for free at chain parts stores. Probably won't even have to take it off the vehicle.

try replaceing guage ,had simular problem with my P30 after guage replacement
problem went away .................

ground sending unit wire if guage pegs replace sending unit if not suspect faulty wiring or guage

It sounds like the voltage regulator is failing.

Are the battery cables good? Any applicable trouble codes? Your generator is computer controlled.

You need to check the alternator regulator. if it lets the alternator go free, it will burn out the diodes.
This is a skilled task. If your not sure get help.

Try replacing the dimmer switch or adjusting it to high. Check fuses, and then the head light switch would be next.

You should be able to download an owner's manual from one of many web sites for a nominal fee. If the battery warning light is on, it could be the battery or the charging circuit (alternator). Check the battery connections first and the battery. If you know how to use a voltmeter, attach it to the battery and see if the battery voltage is around 13.6 - 14.5 volts, indicating that the charging circuit is ok. If the battery is the origiginal, it could simply need replacing.


Note: If you disconnect the battery, you may have to re-program the radio/stereo with a special code. If you don't have this code, only the dealer can give it to you and you will have to prove you are the legal owner.

how low does the oil pressure drop?? is it below 40?

Check the Tension on the Belt First. If it is even a Little loose it will not allow the Alternator to Charge The Battery.