I recently installed a subwoofer with built in AMP (MTX 8" 120W ) on my Honda civic 2012 LX coupe. After the install my headlights dim. I installed a capacitor and that didn't solve the problem. Installation was done by a shop. Based on my research many say dimming headlights can be a grounding issue. The shop have grounded on metal plate that is on top of the frame. Does anyone know where to properly ground a amp in these models?