I have a 2004 silverado just install a nelsons e fan harness and now I got a battery light it flash and say battery not charging now also I disconnect the harness still the same thing. I'm stumped any suggestions?

 

I had the same thing after unplugging the pcm once, didn't change anything on the truck just unplugged the pcm for a few hours...after verifying the alt was actually charging I turned off the codes in the tune and it stopped showing that message...sorry don't remember which codes