I’m good at very few things, you’re the first to say writing. I never tried the 9 volt trick. All my batteries are dead from my son shorting them to his tongue or I would’ve tried that.Lol well at least your a good writer!
My buddy gave me a tip: put a 9 volt battery to the speaker wires behind the deck and you can sort out which wires go to what speakers. Apparently they'll his and pop a bit so if you hear both dash and door speakers hiss we know the answer.