I tapped off of the input of the boot sub to run mine. Tapping off the input of the sub are the instructions of the Model 3 custom sub I installed.
https://nvx.com/products/2017-2022-tesla-model-3-custom-500w-rms-10-subwoofer-bass-package-pbk-tm3-vsw10s2?_pos=4&_sid=f063c0c39&_ss=r