Best Routing for Rear body Wiring thru Firewall?

[DJ_Baar]

Another perplexing question as I continue to install AAW (American Auto Wire) & Classic Auto Air in my '67 Chevy C20.

Its coming along OK, (see pictures,) but not quite sure how the rear body harness exits thru the firewall, or where, and then back down the Driver's side (left) frame rail? Most of the wiring has been completed from these pictures now; all that is really left is a bit more in cab to sort-out and connect (radio, speakers, dash cluster), the relays for electric fans, & front & rear lights.... But could use some feedback on this question.

For some reason I thought it went back like the cab light & fuel gauge wiring under the sill plate and out that corner of the cab. But memory is like the color that faded in my grey-white beard.

I tried to find something with a picture or explanation of this, but had no luck. Any helpful feedback is appreciated.