There are two separate motors. Our 74 Argosy motorhome is setup the same as our 84 310 motorhome, at least physically. The one physical difference that I noticed was the Argosy had stops installed on the bottom edge of the windshield to keep the wiper arms from going down to far. Our 310 does not have those stops installed.
I don't know how the earlier wipers are wired but on our 84 there is a bank of diodes to isolate the wiring between the two wiper motors. I would assume the 74 would be the same but have no proof of that.
I would start by checking your wiring to ensure you're getting power to the passenger side wiper motor when you turn the switch on.
Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)