Alternator Light Stays On

[corfie13]

Hey guys, more electrical trouble with my rig. I finally got my truck running again, took it to a town about 15 minutes away to watch a movie with my father. Everything was fine on the drive over there, came out and the truck wouldn't start. Had to roll start it and made it back home without incident. After some investigation with my uncle who's a bit of a self trained mechanic we determined that it was the alternator. Simple enough, went to NAPA ordered a new one, and put it on the same day. Everything was fine at first, and to be honest everything appears to be as it should at the moment. Except for the Alternator light that is. Strange thing is, with the bad alternator it never came on. Now with a new Alternator the thing stays on constantly . I'm not really too worried about it because as I said everything is fine at the moment. I've driven it sever days over various distances without incident so I think the alternator is fine. Any help would be greatly appreciated, I'm definitely a newbie and need all the help I can get. Thanks in advance.

[amycyclenut]

You can use a multi-meter to take a DC voltage reading on the battery with the truck running to see if the battery is getting charged by the alternator.

Also, from personal experience my light came on after changing my belt, apparently wasn't tight enough. Tightened it, light went off. Maybe it's as simple as that for you?

[Nitekruizer]

You can use a multi-meter to take a DC voltage reading on the battery with the truck running to see if the battery is getting charged by the alternator.

Also, from personal experience my light came on after changing my belt, apparently wasn't tight enough. Tightened it, light went off. Maybe it's as simple as that for you?

Sometimes if the voltage regulator fails the light will come on and other times it won't. I've had it do both when regulators failed, depending on whether it was overcharging or not charging at all.
If you check the battery voltage with the engine idling and compare it to the battery voltage with the engine not running it may tell you. If there's no difference, the system isn't charging. If the system is charging normally, voltage should be aproxiamately 13 - 14.7 volts @ idle. If you're getting upwards of 15 volts and/or if the voltage climbs to 16,17 or 18 volts when you increase the engine rpm, the system is overcharging. I hope this helps.