Every generic harness, even the Painless "Mopar" musclecar harness, pay no attention to the details of your charging system. You are on your own.
Do you still have your original engine harness? If the alternator and voltage regulator are still servicable, try to correctly wire your alternator regulator to field circuits. They are simple. If you split the harness, you can remove the connectors for the blue and green field connections to the alternator that run to the firewall voltage regulator. The blue is tied in parallel to the ballast resistor ignition-on B+. Green is the field control. Then you can treat the alternator output stud as a 1 wire alternator that the harness folks would like you to have. This can also be easily built but the connectors are a little specialized. Francis may sell them, I like real auto electric supply houses like terminal supply co.
Try to get ahold of an A body wiring diagram!
It doesn't sound like you have any original firewall connector or fuse block considerations. If you are working with or around these with your Francis harness you should not have the "chrysler ammeter wiring" problem. (That fix involving adding a second fusible link, dedicated alternator output wiring, and tying together the ammeter leads need not apply!)
