1974 dart sport 360 won’t start with key but will start from starter relay

I have had situations where a car with a fully charged battery starts fine with the key but once the battery charge drops off, the only way to start it is to turn the key to RUN and cross the terminals on the relay. In that case, I blame seasoned wiring. The ignition switch wiring connector is a place that is susceptible to oxidation and corrosion.