I am going to try to explain this the best I can. I have encountered this issue a couple of times and now it is a real issue. The truck is an 01 F150 Supercrew 5.4 gas.
This is what is going on. I can start the truck fine. I however cant roll windows up or down, no heat it wont come on, if I open the door (any of the 4) the 4 ways go off and bright light indication lights up (the 4 ways on outside of truck however are not flashing). Anyone else have this issue? ( note, I have a code reader and put it on just to see if is throwing a code, no codes, but everything I explained above works now, heat, windows etc.) That is until I unplug the code reader then it reverts back to doing all of the above again.

 

Sounds like a bad ground to me. Theyre all over the place. I would start there.

 

Been looking at grounds, hopefully I find it, it drives me nuts.

 

On my truck there is one on the frame by the passenger front door. The reason I mention it is because it’s really exposed and I could see weather and road debris getting to it.

 

The Alternator just went so ill be checking that tomorrow when I put the new one on.

 

That could very well be the issue. A lot of controls are reference signals with small voltages. Any surging could cause issues with those low voltages.

 

Lets hope! I will let you know as soon as I get the new one on, waiting on it to be delivered.

 

Good Morning Brian, I just (yesterday) got to look at the grounds. Wouldn't you know the last one (The one you suggested) passenger side kick area was the loos ground. I would have missed it, but when I took the cover off it arced and sparked a bit so I knew that was it. Thanks for your help.

 

no problem glad i could help. My moms c5 is acting funny in much the same way you described. tried grounds and had no luck. Thinking it in the ignition system. hopefully i can get lucky like you did, and its a quick fix.

 

Lets hope! Ill say a little prayer for ya.