Knowing nothing more than what you've shown and described, I suspect that 702 is an output connector (judging from the other signal at the other pins) with a limited current capability, especially on pin 1 since it's just a control voltage signal, not a power source. Thus the drop in voltage with the load you're applying.
Pin V on 701 (ACC) is the Vcc power in connector, which is why it works as it should.
Could be wrong, of course, but it makes sense to me...