Peugeot 407 Power Wire Routing for amplifier or front parking sensors

[rym]

Hi! I own a 2006 407 SW 2.2 170 LHD, and currently am in the process of fitting the front parking sensors, while I’m at it I’d also like to route a power cable from the battery to the back of the car for potentially installing an additional subwoofer.
I know that the front PDC wiring is integrated into the fog light harness from the factory, the loom then entering the car through the front left of the car(battery/engine fuse box side to be more specific). Does anyone know where the loom enters through the firewall, and how to access it from the engine compartment and inside of the car? Haven’t found any schematics of the firewall anywhere or details. Thanks!