I have a 07 classic ext cab! 54,000 miles and running good! My truck has been fine until last night! Nonnieselman and i were at the house and he had a few newer style pcm's he wanted to read off so he stuck them in my truck to read off! the last one was for a 2004 with a 6.0 and blah blah ya know so he put a tune in that pcm that mine would run on, changed the vin ......all that stuff!
So we go to start it and it just spins over so he checks status and all that but the truck won't start with that pcm......its getting late so we stick mine back in and he goes home! This morning i get in my truck and fire up the truck no hesitation and pull out of the driveway and the battery light comes on! What could cause this? Do i need a reflash or take it to the stealership?

 

well battery is good and so is alternator! So Not sure what to do now! hate to waste the money at a dealership!

 

but the battery light is still on? no engine light? Sounds like the pcm isn't happy with the voltage it is "seeing" does it run any differently? no engine light? I would start with the fuses....