Had the same problem with my buddy's 70 cuda.It was losing IGN 'run' (blue wire) during cranking.With the IGN.switch in the "run" position,check the voltage at the red wire (batt.)and the blue one,coming from the back of the switch. It should be within 1/2 volt of each other.Then disconnect your yellow wire on the starter relay,so it doesn't effect your readings,and check it again in the "start" position I don't know what to recomend,as I replaced it with a new switch from NAPA and had the same problem 1 month,150 miles later