Like this?
Way I did it was using a servo on an open channel and a 2 way switch on TX.
Equipment:
1) Telephone wire (used in houses)
2) Cheap, small servo
3) foil or tabs
4) small washer
5) Estes igniter
I use 3 cell lipo for system. I used 1 cell of charge balancing system (3.40 volts) for your plus-minus. Do not hook to 12+ volts
So circuit is + wire out of 1 leg of balancing system which goes to servo arm. I soldered a metal tab to wire located at end of servo which is held on by hot glue. Switch is left position 1 so servo is up and not connecting and loaded..
Telephone wire is soldered to another tab and placed so when tx switch is flipped, servo arm comes down and makes contact to complete circuit. Use hot glue to position say to fuse and then the wire goes to + side of igniter. Use
ATV in tx for travel.
Negative side of igniter is connected to more telephone wire that runs back to negative side of the first cell of lipo to complete process.
Concept is system goes hot when tx switch moves the servo arm to position 2 and makes contact with the other tab.
Called AMA, mine was legal and allowed.
Immediately after flipping the switch, I turn off the switch to prevent any chance of 1 cell drainage if somehow it completes the circuit. Works for me. I used it 5 times with no problem.