I'm currently cleaning up all my wiring and connections, fixing things that need fixing along the way. The FSM (for a 72 Valiant) wiring diagram has been extremely helpful, though it's still a tough slog. Someone did a crappy black spray bomb in the engine bay a long time ago, covering the true...
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A parts book and a shop manual will help with these things. You can buy used or reprints or CD versions from places Bishko and also in the for sale section here.
There is a scanned 72 Plymouth manual here (free to download) MyMopar - Mopar Forums & Information - Service Manuals
If you need help working with the diagrams, let us know.
There's also a Master Tech on working with diagrams in '68
A good index of the master Tech Conference is at the Online Imperial club
The Imperial Mailing List Online Car Club is dedicated to the preservation, appreciation and restoration of Imperials and Chrysler Imperials of all years, models and body-styles.