A few things to check, the wires can become broken internally on the t2 cannon as they commonly do in the sttng cannons, resulting in them only being capable of firing when it is in certain positions of its rotation so check for that. You said the coil fires in test mode is this with the gun in exactly the home position and not pointed towards targets? That would indicate this may be your problem.

Also another possibility the plunger gun handle switch is reset by a spring that pulls the rod back into the handle if the spring is crushed or worn out the rod doesn't retract quickly or smoothly so can result in the switch being closed and not firing the cannon until it retracts completely in the gun.