Make sure you know the build date of your car, or better yet, remove the old harness and count the the wires before ordering the new harness.
When the 1970 models were first built, the front, under bumper parking lights were wired on a separate circuit from the side marker lights. Ford made a wiring change in the fall of 1969 and put all the parking lights on the same wire, eliminating one wire from the underhood/headlight harness. The reproduction harness for Mach 1's built after 10/15/69 only has 10 wires, the early harness has 11.
An early harness will not power the front parking lights in a late car, but the late model harness will work in to power all the parking lights in all 1970 Mach 1's. The early harness disabled the front parking lights when the sportlamps were turned on.