HumpDay

New member and aspiring basshead here. I have a system planned out for my 04 silverado. I haven't done the math and I'm pretty doubtful the 250A alternator I have won't cut it for the 3920 RMS the system will be pulling. I'm considering doing a dual alternator setup including the original alternator, but the wiring harness is confusing me. I understand that the second alternator needs to be excited from an ignition source (brown wire), but I'm not sure what the gray wire is for. If I could get some help on whether or not this wire is necessary for my aux. alternator it would be appreciated.