need help with an electrical issue-PLEASE

I have a friend who is bagging his 95 sonoma and relocating his battery to the bed. I told him to replace the wire from the poisitve terminal to the distribution block with a bigger stereo type wire and run it back to the bed, but he can not find where that factory wire goes from the battery terminal. is is the 4 cyl engine. any ideas on what he can do? a good indepth answer would be very appreciated.

Hook it to the starter. Thats where it should go anyways.

one I get mine aired up I will let u know. U can use some 4guage for the pos.

ok maybe i wasn't clear...we are trying to replace the wire with a bigger one but when we trace it back it seems to go into a cluster of wires and can't find out where it goes....how do I safely add a 4 gauge wire to run it back to the bed? I know it obviously has to connect to the starter, but i'm confused from there on.....