Hi everyone, first post here

I am currently in the process of installing an amplifier under my passenger seat, connecting two coaxial speakers (rear) and two new component speakers (front) at 4 x 100 Watts RMS. I need to run new wiring to all speakers because of the new power.

I removed the factory front speakers in prep for the new speaker installation and just left the factory speaker wire harness hanging free. I guess this was a crucial newbie mistake as I started the car today and it was in complete disarray (aircon cut out, multiple dash warning lights, speedo and rev gauge not working).
This all cleared and the car ran fine after reconnecting the speaker.

I'm wondering now, how can I safely remove the factory speaker wiring and run new wiring to the speakers without the car s**t itself?

Furthermore, does anyone have any advice on the best place to install the crossover in the door?

I am fairly new to car audio installations, thanks in advance!