JVC Arsenal KW-ADV790 missing parking brake wire

[butterMilk 10+ year member]

My buddy just bought a new car that already had the JVC HU installed in it. He told me that when he tries to watch a movie he can only hear the sound. So I went to check it out, and took a look behind the HU at the wiring harness. The wiring harness is missing the Light Green parking brake wire. I looked at the owners manual and it showed the harness and all the wires going into it, but not which wire went to which pin # on the harness. Oh yeah and the harness has 3 empty slots, pin # 4,13,14

Anyone know how to find out which wire belongs where, or what going on here?

EDIT: Its actually a ADV793 not a ADV790

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