Backstory: 96 Cherokee 4.0L auto trans 2wd
had some transmission trouble, and decided to fix or replace it. Long story short it has been sitting untouched for about 2 years until today.

today: Slapped a used transmission in it and a new battery and got it running surprisingly very well. After sitting for 2 years it runs rough-ish, but all in all I could not ask for anything better. BUT the gen light is on, and aside from maybe the alternator idk what would be causing it to pop that light. Drove it from where it had been sitting in the next town over all the way home (about 10 miles) and had no issues as far as lights, or radio cutting out. Again the ONLY thing I did was new transmission, and new battery.

what should I be looking at that could pop that light because until tonight I’m unfamiliar with it. Thanks for any help!