Greetings!
At the bottom of your fuse box diagram, there appears to be a large stud at the bottom center for power going into the fuse box, and it says to put a fuse in that line of a max of 125 amps. So your cable should be sized to carry 130+ amps @ 12 vdc and it should connect to the stud with a ring terminal.
The Y is an equal sized cable, also with a ring terminal on the end and equal fuse. It attaches to the same stud at the fuse box.
Cheers!
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