Just finished my double stacked triples subs (6 drivers per side). Use my trusted 9V battery polarity tester to verify correct wiring.
I made this 15 years ago and it consists of a 9 volt battery, a intermittent button switch and leads out of the small (2X3" approx) project box
All driver go forward with + lead to red terminal. ALSO the servo coils will give forward motion with + to red (much less motion to 9V DC signal then main speaker coil).
Very simple trick. I have several complex systems and this tool gets used ALL the time.