My alternator takes about 90 to 100 seconds to start charging after starting. (every time). After it kicks on, everything is fine.
It is on my 2000SS with an E38 stand alone harness. The alternator plug on the 2012 Silverado harness is a 2 pin plug, so I used a 2 pin plug alternator. There is no BCM.
I don't know how it is controlled thru the computer. Or at all. Thanks for any info
DW

 

Under System, there is the alternator section (E38) and the top tab asks if it is voltage control fitted. I do not have a BCM so I had to change it to ( Not fitted).