Once you have the harness in hand with the dash in front of you it becomes pretty apparent where and how it routes.
I do have few pictures of a 71 harness as the later harness are a bit different expecially the 74 with seat belt interlock. They all route the same way.
74 dash laying on the cardboard. 71 harness laying on the concrete.
The 71 harness being installed in the dash. It's not that hard at all to remove the whole dash and makes this job 10X eaiser.
This is what it looks like after you pull the dash.