Believe this was one of those dealer installed options so location and routing will vary depending on the kid that the dealership had installing them
Checked my pictures (both 69 & 70's) and it does not seems to have been a very popular (like most years) option/accessory. Only picture I can offer is the one below from 69's
69 San Jose built car
69 Dearborn built car
routing appears that it may be the same though mounting location differ
Hope this helps a little