LLY: Batteries not charging

[TBSK]

I have an 05 Duramax with 155,000 miles, runs and starts perfect just replaced water pump and the other day battery light came on and the info center saying battery not charging. Took it into dealer they put it on the machine it told them the PCM is not telling the altenater to charge batteries. So I bought a new PCM, put it in and its still doing the same thing. Any suggestions? Before I spend more money..

 

[MACKIN]

So the dealer cannot figure it out? What voltage are you getting at the batteries with truck running?

 

[MACKIN]

Oops check all connections at the alternator also.

 

[DIGGLER]

isnt there an "alt" fuse in the fuse panel? if so, may want to check that. should be like a 10-20a fuse for that i was thinking...