why are my speakers bridged?

So im doing an aftermarket speaker install on my 1997 jetta and so far ive been puling my hair out. Heres what ive found out. in my front door panels there was a regular speaker, this speaker ran up to a 4ohm tweeter, then to the head unit. so that tweeter has 4 wires total running to it... i checked how? i hooked up a 9v to the + and - terminals on the door speaker and it came up 9v on 2 of the tweeter wires, (oddly the door speaker wires and the receiving wires on the tweeter are different color) then when all 4 tweeter wires were connected the output wires behind the HU read 9v.

can someone explain to me how to achieve getting the aftermarket speakers i plan on putting in connected to 4 channel amp?

ok what speakers, HU, and amp?

Pioneer D series package. 2 ways in the front with tweeters and the other two in the back. Amp. I have one PX3200D for subs and a PX4.1600 for my speakers. My HU is a JVC KD-S37 or something like that.

The tweeter in your dash is connected to the speaker in the door through a crossover.  If you want to reuse that location you should run new wiring.  If you want to try and reuse some of the factory wiring you should check continuity end-to-end with an ohm meter, not using a 9V battery and volt meter.

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Yeah I decided to rewire.. I had to split 25 ft of speed wire.. Is there any way to keep my two tweeters in the back powered by my HU, or should I get two more Passive crossovers to run them from my rear deck speakers. So total I have 2 tweeters in the front, two door speakers in the front, and the same In the front. All on a 4 channel