Also check the two main alternator feed fuses in the PDC (Underhood relay center). If someone jump started it backwards it may have blown these two fuses. Usually they are 60 amp Maxi-Fuses.

If you need a new alternator, a 120, 135 or 150 amp large case alt off of a ZJ is a bolt on! You may need to swap the pulley and main wiring insulator if you get one for a V8 instead of a six. Be sure to upgrade the two PDC fuses if you get the bigger alt.