Hi Trevor,
Nothing worse than getting something new and it is faulty
So the combined voltage at the battery holder plug should be 4.2 volts offload, and when plugged into the ignition and turned on i would guess you would be looking at 3.8 volts? If the voltage is lower check the obvious like reversed connector etc. also check the power on the other side of the switch in case the switch is duff.
Maybe the batteries are not so good, but 1.4 volts is not far off the mark, it is the on load voltage that counts, anything over 3 volts should be fine.
How about the hall effect sensor, no pinched wires? disk on the right way around (air gap not too big).
Banggood sell replacement ignitions for about £35 but i guess if all looks ok it should go back under warrentee.
Ade