Get a 1970 Plymouth Service Manual.
The pdf scans here will get you started in most cases. If no Plymouth there, Dodge will be close.
MyMopar - Mopar Forums & Information - Service Manuals
Bishko is a place you can buy one.
Go to the back of the electrical section and you will find the wiring diagrams.
Many TSBs can be found in the
The 1970 Hamtramck Registry Library Page (1970 - 1974)
Those have have updates and corrections.
And lots of Chrysler Tech tips here
Master Technician Service Conference - Chrysler's Training for Mechanics
Including a several about wiring diagrams and power, ignition and accessory circuits.
Color coding:
Both Black and Red was used for the main circuits and many feeds.
Generally Chrysler had a consistant use of wire colors but there
were changes over time.
Main Circuit:
The main circuit consists of two power sources, and a feed from each that join under the dash at a main splice. Power from main splice is distributed to the fuse box, key switch, and headlight switch. These wires are always hot when the battery is connected. There was a fusible link to provide a bit of protection from accidental grounding of the battery.
Power for the horns may be from a different location in '70. Also will be hot at all times.
When people add stereos and other electical devices, they often tap into the main circuit.
Also may have tapped into the Run circuit????
Original ignition and charging circuits for 70-71 would be something like this