Battery light on start up.

[bigblackF250]

As the title states, when I turn the switch on the battery light indicator comes on, does not matter if glow plugs come on or not the light still comes on. I have both new batteries, I think they are 950 cca each, I cleaned all the terminals, cleaned the grounds, etc. The light goes off as soon as the truck starts. What else could I look at that would cause this? The starter does seem to drag a little but not enough to make me think the starter is dying.
thanks, Rob

 

[BROWNIEBOY525]

the battery light coming on then is normal

 

[Cincinnati Guy]

Yes its just completely normal, I guess just an indication to show you the light works...

 

[bigblackF250]

Thats wierd, maybe I just did not notice it before, really only noticed it coming on like in the last 6 months.
Thanks.

 

[spyder1100]

The light comes on if the voltage is less than 12.5 volts. After you start the engine, the alt starts charging at (hopefully) 14 volts, causing the light to go out.

 

[icanfixall]

That lite is there to show you two things. First is when you turn the ignition switch to the on or run position it tells you that the lite is not burned out. Secondly it tells you that if the motor is running and the lite comes on then you lost the belt or you are not getting enough voltage out of the alternater. Funny how things just show up that you never saw before. Happens to me everytime I'm looking for a certain wrench. I have three of every wrench I need but can never find one easily when I need it..... CRS I guess.

 

[MUDKICKR]

the funny thing is if that light doesnt work, the alt wont work either. the alt has a neg field when it isnt turning. when you turn the key power goes to the light bulb from the ign switch. since the alt isnt turning its neg. field makes the bulb turn on. when you start the trk and alt starts turning, which turns the neg field into a pos field (charging battery) and then turns the bulb off. the reason the bulb goes off is the pos field puts power to the bulb. so now both sides of the bulb is power and without a neg the bulb goes out. also if the alt goes bad, it makes the light come on due to being a neg field. (not charging)

 

[bigblackF250]

Well that is good to know, believe it or not I have owned this truck for 11 years and just noticed this light 6 months ago, probably been coming on for years, who knows.

 

[BROWNIEBOY525]

i did the same thing i had mine for almost 3 years now and just noticed the light coming on a few months ago