Battery Warning Light

[webster4040]

Battery warning light comes on under a load. Battery not too old. Any suggestions on how to determin if it is the battery, alternator, or something else. Truck is 99 F250 Superduty.

[Davescort97]

Usually when the bat light comes on it is the alternator not charging. If you've got a volt-ohmeter you can check it. The battery should have 12.8 volts not running. Running at idle the battery voltage should be at least 13.3. Running above idle with accessories on the alternator should be putting out around 14.3. Check your belt. It should be tight enough to only deflect 1/4 inch when pressed upon with your hand.

The Ford alternator has a voltage regulator outside the case with the brushes attatched inside. Not always, but most of the time the brushes will become so worn that the springs won't hold them against the armature with enough force for current to flow. Brushes are cheap compared to the price of a new alternator. Under a load the brushes would fail.

[webster4040]

Thanks for the info. It was the alternator.