Bought this 2009 ford f150 fx4 5.4l and when I was driving home it was fine then the next day it was having problems turning on and it had the check charging system light on so I went to auto part and they said I needed a new alternator and so I bought one and installed it and it still has the check charging system light on so to check if it working properly I disconnected the battery and the truck turned off so does that mean that the car was running off the battery and the alternator is not charging the battery? I’ve checked all the fuses and relays and they are all good so I’m guessing maybe it’s a broken wire from the alternator but so far everything looks good nothing looks broken or burnt or stripped wires so I’m lost

 

Welcome to the forum. Here is some help on diagnosing alternator issues.

 

Fords are very finicky about alternators. Was the one you installed a Motorcraft or 3rd party?

 

I bought the one they said in auto zone

 

Probably a Duralast or Duralast Gold then. That's their in house brand I think.

 

More than once I've got an alternator that was bad out of the box. Have you put a volt meter on it with the engine running? What is the output?

 

this, could be bad out of the box, voltage test will help verify.

I also remember reading about some of the 5.4 trucks and issues with aftermarket alternators causing the light to come on even though they were charging correctly. I saw similar issues when looking for one on a friends 2006 I think it was. I put a Duralast on hers from Rock Auto it worked fine.

 

Yep, the guy on youtube, Ford Boss Me, before he left the Ford dealership was working on a Crown Vic I believe. They did not have any alternators in stock for a repair, so he was authorized to go outside and buy the alternator. (After COVID) I believe he went through 3 before he got one from NAPA that tuned the battery light off in the Crown Vic. Also as an FYI, he stated that when they are authorized to go outside for a part, it carries the same warranty as if a Motorcraft part was used.

 

there is no output I tested continuity on all three alternator wires and only the purple wire gave me OL is there a diagram for that wire so I can replace it all the way from the pcm to the alternator like a pinout diagram?