Ignition wires

Those diagrams aren't too bad "for some things" but they are not always complete. Do yourself a big favor and go back to "MyMopar" and download the factory service manual.........which is also free. By the way, that 72 manual and several others over there came from guys on here at FABO

The two wires you want are accessible from the column connector leading to the ignition switch. Here's a crop out of page 8-150, 151

You want the 3rd and 4th from the top. Dont cut the blue, as it feeds "other stuff." Tap into it, splice, crimp, solder, whatever.