Still confused.
Can someone clarify on how the wires leave the stereo and reach the door speaker and then the tweeter on a standard non-amped, non HK set up?
I can only comment on the Euro E46 Vert with non HK and no amplifier.
It has an inline resistor connected to the cable/wiring from the bass/woofer speaker to the tweeter, see the circled area in the photo:
I cut and soldered spade connectors for my set up :
and shrink wrapped in the final install:
Then shrink wrapped the spade connections after fitting for good measure:
Obviously you cannot use the same / original tweeter cable with new tweeters if you want to use your own crossover because of the inline resistor.
(Unless you replace them with identical 8ohm tweeters - but then what was the point ?)
So in summary, the woofer / bass cable can be cut and soldered and the tweeter wire is best replaced. Any crossover needs to be wired in the door (or take a feed from before the amplifier - if / where the car has one)
Hope this helps, it shows where my crossover is in the door between the woofer and tweeter. I have a non HK and no factory amplifier set up. The speaker input feeds the crossover and the crossover has a tweeter output and a bass/woofer output which you connect to the corresponding speaker:
