I recently picked up a 99 Suburban, 197K miles, barely broken in...I have a couple underhood questions:
There is what appears to be a factory installed secondary battery tray, and there are two positvie leads off of the battery. what is puprpose of this second tray?

Also on my radiator, just below the filler neck, there is a roughly half inch nipple that is capped off, any idea of the purpose of this additional fitting?