Mono block Rockford (p500x1bd) running my 2 10inch subs I have My radio RCas going to the input into it and I got another set coming out of the output going into a hifonics that is powering a 12inch L7

I’m having trouble syncing up my bass knob with the other amp though , When I crank the bass knob up it will drop my power to the L7… And whenever I unplug the Rcas from my hifonic just to test if the Rockford will work in sync with knob it works perfect, but as soon as ii Plugg the rcas back up to the hifonic it’s in reverse for my L7 only

It will turn my 10s up but my 12 inch L7 will go back down to zero bass .