Low charge to no charge issue pulling hair out
Here's my tips for the repair.
If available download a 1973 Dodge or Plymouth Service Manual. Most of the wiring diagrams will be in the Chassis manual. Some of the body harnesses and extras will be in the Body Manual.
www.mymopar.com -> service manuals
Your car probably came with standard harness but there were heavy duty and fleet optioned cars. I mention it for two reasons.
1. Some of us have borrowed the wiring concepts used on those options for our own cars. It is more work, but something to consider.
2. The reddish wire going into the multi-connector looks pretty fat. Its possibly a 10 gage wire, and its possible your car has some heavy duty wiring. However usually when heavy wiring was used instead of going into the multiconnector, they used a locked bullet connector and then a grommet through the firewall.
I don't know if '73 Shop Manuals will have any harness illustrations. A few years have them, or have them for options and accessories.
If you're really interested, Faxon has some factory assembly drawings which will show the harnesses and where to attach etc, but don't know if they have your car and year. If they don't, don't bother.
There is some good info here on FABO about making splices, and replacing terminals.
This method can work with or without soldering.
https://www.forabodiesonly.com/mopa...ips-from-the-dodge-ram-service-manual.432623/
https://www.forabodiesonly.com/mopar/threads/clever-splice.447928/
In the engine bay I try to use wire and heat shrink with oil resistance and tolerant of higher heat.
I live close enough to a marine supply that sells wire by the foot as well as in small rolls, so thats a source for me.
In the passenger compartment, general purpose automotive wire will work fine.
Here's some threads about crimping wire terminals
A bit of Wiring 101
Checking crimps
Lets Talk Open Barrel Crimpers - Reviews and Discussion
When done, rewrap the wires in a nonsticky harness tape and secure in the original holders so nothing chafes.