Ok so meter reading 2 & 3 show the potential for current flow, but not the current flow that should be. Which would be the reason that you are getting only half of the voltage.
Looking at figure 1, with the given info, meter 1 show that there is an open circuit and there is no current flow. Now meter 2 and 3, show a closed circuit showing the correct voltage for each line to N.
For the igniter the current would go from L1 through ignitor through detector to N. That the current is going around the main as there is less resistance through the detector than the main coil.
