I worked on a L99 with a flickering battery light several weeks ago. The owner changed out the batteries and alternator and the battery light went out and stayed out for a month or so and then it came back on. The owner then installed a new alternator and the light went out and stayed off for several months and then came back on. I was called to repair it. I load tested the batteries to make sure they were good and both batteries checked good. I then bench tested the alternator which passed the testing. I then suspected the tensioner and replaced it with a new one and a new idler too. The tensioner that came off was the original Ford part with 156,000 miles on it. After the repair the battery light went out and stayed off until last night when I was informed that it had come back on. I don't know where to go from here.

Has anyone had this problem? Could the battery cables be the fault? The truck has an alarm installed but hasn't worked since they truck was bought by my friend. That's the only aftermarket part installed. I need some help and direction here..

Thanks,
Jeff

 

Does the battery light only come on at idle, or at road speed, or both? Here is a good troubleshooting flowchart...

EDIT: I just emailed you a pdf document you might find handy.

EDIT EDIT: Here is a good page...

 

Thanks Neal.....Don't have the truck yet to check out. I'm busy this week. Probably won't get it until next week.

Jeff