The MyMopar diagrams are not always correct, and not always complete. They are far better than nothing, and for some problems, easier to follow than the factory ones. Generally, Dart, Valient are pretty much the same except for Rally Dash cluster, etc
There's a 72 shop manual posted over at FABO, but there were changes between 72 and 74, and I'm not sure whether 73 is closer to one or the other. I have a paper manual for '74, so that's a PITA to post material online.
http://www.mymopar.com/downloads/1973/73ValiantA.jpg
http://www.mymopar.com/downloads/1973/73ValiantB.jpg