Hi guys! I have a 2014 Cadillac ELR and I'd like to upgrade the sub that came with the car. I'm not looking to rock the town but I'd like to hear it when I'm standing next to the car. I bought an Infinity Primus 3000a amp and paired it with an Infinity Kappa 800W 8 inch sub in a sealed box. Unfortunately it doesn't hit any harder that the pancake sub that came with the car. I'm thinking I must have something wired up wrong. The amp has RCA input and a high level input. My car doesn't have RCA outputs so I used the high level inputs. They have +/- wires for left & right channels and a ground wire. However the connection at the sub that came with the car only has two wires. How do I properly connect this?? Originally I connected the "+" of the high level left/right channel to the "+" from the car and did the same with the "-". Then I tried connecting only the left channel +/- to the sub wire and it worked but not loud. Then I discovered I just just connect the + wire to one of the car's wires and the sub still worked. I don't know what I'm doing.... Help! LOL