I did not have to tap power using high level inputs the sub has an auto on/off switch that detects audio, I am using a all in in one unit from Rockville, ground is 8 gauge to one of the anchor bolts behind the rear seat, power is also 8 gauge, speaker wire is 16 gaugeFirst, you don’t have a good bass signal at the rear speakers. They are bandpassed. Front speakers get full signal but are attenuated below 100-80 hz. You need to tap into front speaker signal and use a bass restoration device. Audiocontrol makes a great one. What amp/sub combo do you have ? Where is it grounded ? What size ground and power wire ? Where did you tap power ?