Put a new alternator in 2000 Jeep Grand Cherokee engine light on

Well , the ECU runs the alternator. (DG wire "dark green")
the alternator field is controlled 100% by PCM reg , inside PCM.
so..... if the running engine has 13.3, to 15vdc the alt is working
if lower, its not. (rpm on engine 800 or more)

not scanning the PCM a the CEL glow, you missed the boat.
why not scan it. see why the PCM is upset (DTC errors stored)

see the 2 lower pins below , those go to PCM.
in theory if the field in the old BAD ALT, was shorted.
that could in fact, burn up the PCM regulator.
shorting outputs of PCM , does that in most cases.
im the poor sod that fixes PCM's.so....

If the battery is been tested and is good then the ALT .must be chargeing it .
Try these 2 tests volt meter veh. running top bat . terminals 20 V dc scale B to B R to R you should at least 13 dc v 14 to 15 v is better but if your over 13 the ALT is chargeing the bat .
# 2 test disconnect the NEG. cable from the BAT. meter on same scale 20 v dc .Go R to R on BAT. and B to engine ground engine block any metal that isn't painted that bolts to the engine or frame .
If you read voltage you have a short someware in the vehicle .The B+ side hot power is comeing in contact with the negitive side ground .With the negitive cable disconnected from the battery their should be no path so the problem is something that bolts to the engine or frame must be shorting interinally .
My best guess would be the starting motor see what you get because all I can do is guess at this point .

Test the alternator charging capability by connecting a volt meter to the battery terminals and starting the engine. The voltage should be at least 13 VDC.
If it's less it will not charge the battery enough.
Hope this helps.

Ive had this similar problem in the past with my 2000 Grand Jeep Cherokee. Ive found by putting the Jeep in neutral ...it started right away. Good luck