With a '75 Manual there 's at least a couple approaches.
Knowing nothing about the wiring, one approach is if its the engine bay to look at the CE diagrams and see which ones match. It's only a couple pages and the drawings are pretty clear.
Another approach is to look at the wire insulation colors (and sizes) to see which circuits it might be. It may be neccessary to wipe some of the grime off the wires. The manual has list of circuit names matched to the colors. Bugman posted a photo of it from '75 in post 26 this thread.
https://www.forabodiesonly.com/mopar/threads/ignition-help-needed-stumped.499412/post-1973584589Combining the two ofcourse is also possible.
The more you do, the more you learn.