Here’s the prototype
Note red wire +7.2v, blue wire is 0v, black wire is signal.
And here’s the schematic.
The issue with the HL High Tension flash unit is it requires a +7.2v trigger signal where everything else in the tank uses a 0v trigger signal. So all this does is take the 0v signal and changes it to a +7.2v signal.
In the above example I have used the Tamiya recoil port to pick up the signal and voltage, but you could take the voltage from the power supply cable and the signal from the airsoft/recoil wire also.
Note the HL High Tension flash unit comes with a 5 pin plug. You only need the 3 wires which actually go to the flash unit the other two are no longer required with this setup.
Hope that helps.