2012 Western Star charging problem

Follow the pink or red wire from the plug on the alternator to the alt sensor the wire is very likely rotted or chaffed through some where between

 

Follow the red wire or pink from the alternator to to load sensor on the firewall that wire is likely to be rotted or chaffed through I just fixed one today that's what I found

 

The alternator probably is a remote sense alternator. Remove the small wire from the alternator. Check it for voltage. It should match battery voltage. Do not use a test light. Use a volt meter!!! if the voltage does match pull and tug on the harness from the alternator all the way back to the PNDB. That is where the remote sense fuse is located. Also remove the connector from the PNDB and check for spread pins. Remove the fuse from the PNDB and check it for corrosion, and spread pins. About that year model of PNDB had a known problem of the terminals for the fuses becoming spread and the fuse would fit loose. If you don't have anything to check for spread pins in the PNDB get a ATC fuse and cut one of the legs off with a pair of dikes and use the remaining leg as a drag test tool. Also make sure the wire was connected to the remote sense terminal on the alternator.