Well, after comparing a variety of underdash harnesses from my stash, I found the following.1969/70 non-AC cars: the heater box connector breaks from the passenger side part of the harness below the break-out of the turn signal flasher and the door jamb switch.1969/70 AC cars: most have the heater box connector breaks out at the turn signal flasher break-out such that that section of wiring can reach the left side of the heater box. Rarely seen in 1969, I do have a tach dash version like this. This variant will also fit a non-AC heater box just fine, as the wire lengths are identical between the two variants.
1969/70 AC cars: some have the heater box break-out in the section going to the firewall grommet with a molded 3 pin flat bullet connector. An extension harness plugs into the 3 pin flat connector ending up with the standard "rectangular" 3 pin spade connector. Rarely seen in 1969, I do have a tach dash version like this. On rare occasions, I see a further extender from 3 pin spade to 3 pin spade. These extenders are fairly rare.1970 AC cars: I've seen a few cars that have both the rectangular connector down near the turn signal flasher break-out AND the 3 pin flat connector breaking out of the section going to the firewall. Two sets of wires for each (red, blue, and black/yellow) are in the heater switch connector.
I'm not sure why there are all these variations, as the second version could be used for both AC and non-AC configurations, saving Ford manufacturing costs and inventory. I'm sure there's a good reason, though.
I have converted non-AC 69/70 harnesses at least 2-3 dozen times in the past without changing wire routing, and only had two complaints with fitting AC boxes, one of which was a Cougar. These kinds of subtle variations are hard to pick up unless you compare them side by side. At least from here-on out, I'll be doing to changes correctly.
Randy
