Cat 287b charging problems

My 287b is not charging. I replaced the alternator and both battery cables. I cleaned to electrical connections when I did that. The battery has good voltage and load tests good.

Which wire in the 4 wire plug on the back of the alternator is the exciter wire (12v power/ trigger)? I want to test to see if the alt is being told to charge.

Thanks in advance.

Cat 287b charging problems