02 F250 7.3 battery light just came on, is this indicating a bad alternator or battery. Other than the light there are no symptoms so far

Contrary to popular belief, the battery light can be on even if the battery and alternator appear to be working fine. It is located in such a place as to indicate effective charging. What that means is that even if the battery is good and the alternator is outputting voltage (and current), the lamp lights to indicate that the vehicle is consuming more power than the alternator is producing. This is important since once running, if the alternator cannot supply all the vehicle's power needs, the battery is drawn on for the remainder, and will suffer draining as such. Most manufacturers provide alternators that produce more than enough power to operate their vehicles, but many owners add additional high-power audio systems and other items that can overwhelm the factory unit.

You said the alternator was "tested"....was it load tested, or did they simply hook a voltmeter to it while the engine was running and saw 14.5 volts? This is important since a failing alternator may regulate its voltage properly, but may fall far short of the output current (power) needed to operate the vehicle.

It is possible that there could be a defect in the battery amp circuit, but it is such a simple circuit that I would be more suspect of a charging system issue than I would of a faulty battery light. And no, there is no reset for it - as soon as the power balance returns to the positive side (car needs less than is produced), it will go out all by itself.

A bad alternator or charging system will leave the battery low lights dim, should have the no charging indicator light on the dash and the car will eventually stop running as the battery looses its charge. Maybe you can tell us your problem and we can give you some mor info.

bad alternater or wiring problem!!!

you need to check voltage at the battery with the car running. The battery light indicates there is a problem with the charging system not necessarily the battery but the alternator. With the car running you should see more than 13.5 volts and better yet over 14 volts. if you see around 12 volts or less than you have a charging system problem and most likely the alternator has gone bad.

Have you notice any other symptoms like the loss of power steering or the engine overheating?

When you changed the battery did you check the cable ends to make sure they where nice and clean?

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doug hard688, It sounds like you have an alternator issue here. The volt meter monitors the output of the alternator. The battery indicator will come on when you have a bad or weak alternator. When this happens you are running on the power of the battery alone and this does not last long. As you state here the radio quit working and your lights probably got dimmer with time. As far as the other lights coming on, when some systems don't have enough power to run them the lights will come on indicating a problem. I wouldn't worry about them until you have your charging system checked. You can do this yourself if you have a volt meter. Start the vehicle and put the meter's red lead on the positive terminal of the battery and the black lead on the negative side. A properly charging alternator will be putting out 13.6 to 14.6 volts. A few tenths of a volt either way out of these specs is nothing to worry about. However, a variation really far from these specs indicates an alternator problem. Good luck with this.

check alternator pully for play. Symptoms indicate a bad pully bearing allowing the belt to slip off. Could be other than alternator, such as an idler pulley or the tensioner, but you mention the battery discharging, which also indicates alternator.

The battery light is usually an indication that the battery is not charging. This could mean your alternator is bad but sure to check the alternator belt tension carefully. If it is loose, it can make the alternator appear bad.

You didn't provide any information about the symptoms that let you think your alternator is going bad or bad.
Starting problem? engine stalls? weak lightning? electrical cutoff?

Without these info itcould be hard to provide the correct answer.
If it's bad you should have a red light indicator in your dash indicating problem with the charging system.

If you have a charging needle gage in your dash it should indicate somewhere in between 13.8 and 14.2 volts engine running and different accessories turned on (heater fan, headlamps, rear defroster etc...I do not have specific specs for your vehicule but I should be pretty close.

On top of it, you could take precise measurement using a voltmeter at the battery terminal when the engine is running.

Below that lower limit, it could indicate it's bad or going bad not providing enough electrical power to keep the engine and accessories running and to recharge your battery for the next engine start.
At a certain point, if it's too low your battery will have to compensate and provide power what it's abnormal once the engine is started. Under these conditions the battery will gonna die and the engine will stop and not restart.

This is a short and simple verification process description.
Depending on you problem symptoms, you could also check the serpentine strap condition, battery terminals for corrosion, the battery condition by itself or have to go in a more in depth verification if problem still there..
If it's the original battery, it potentially reached the end of its life. Good idea to have it checked. Just checking its voltage is not sufficient. It requires a 'load' check.

Do not hesitate to ask additional info, providing more details if it's not answering/solving problem.
Hope it will help
Dan (sorry for my english)

Could have a bad battery,or the alternator could be going bad,would have the charging system checked as well as the battery.Most auto parts stores have a tester that can check this for free.