What wire goes where off a and b stud to power distribution a and b

at the a and b studs, that supply power to the maxi fuse section and the mini and relay section of power distribution box, _{, how do you know which wire goes where on top………….. the maxi fuse has an a and b bolt to connect to, also the box with relays and mini fuses has a stud on both sides} marked a and b.

ive read that my lb7 has battery one which is to ecu and starter_{,, and the 2nd battery known as the auxillary battery is after diesal starts 2nd battery is for this},,,, also states there is a iso( isolator) keeping 2nd battery from draining battery one…….

need to know correct connect _{,, when i got the truck the thick red wire and medium sized red wire appeared to have been mended together and broke}, therefore leaving me not knowing what went where.