For last few months I have been having an issue with my battery light turning on and off. When it turns on it adds an extra draw on my electrical system and then it just shuts off and the draw goes away. I took out my alternator thinking it was going bad, and took it in and had it tested. They said that there was no problem with the alternator, but they would be happy to sell me a new one if I wanted. I put the alternator back in, the problem would come and go, and was more annoying than anything. Recently the battery light came on and didn't go off and completely drained my battery. Any ideas on what it might be?

Thanks

 

Model and year of truck?

 

97 expedition 5.4 eddie bauer

 

If you are getting a battery light then you should be able to pull a DTC. However, it is very likely your alternator. When it doesn't output current, light comes on and your battery provides all the juice.

 

Battery light usually means an alternator problem.

 

Just a SWAG.

1. Check that the fuse for the alternator field is not loose in the fuse slot.

2. Check that the alternator field harness is not crapped up. This is some what common.
thread on the topic ( of a non working field connector ) and JBrew's reply and pictures :

https://www.f150online.com/forums/el...nator-why.html

 

I had a similar issue not too long ago. Light came on when I was on a date with my Fiancee, so we cut it short and went home. Couldn't find anything wrong. Truck ran great. 3-4 weeks later, the light started showing up again, constantly. Replaced the alternator based on a suggestion from my dad, and it fixed the issue.

 

Read this caption:

 

Um, no. The PCM has no way of knowing there is a charging system problem on his truck.

It's going to be a problem with the alternator or its associated circuitry.

 

Yep correct, forgot we are dealing with an I-line warning lamp setup unlike the smart charging systems on '04MY's and later.