I just got a sub box and amp. I already have a amp installed for factory sub. But I'm changing out to the new one. The amp I had previously is a 2 channel amp and the new one is a mono amp. I hooked everything up and I get no sound using new amp. I've checked everything I could think of and still no sound. If I hook up my old amp you get sound out of subs. The reason I'm changing is its a bigger amp and a pair of subs. I don't know what else to check, any help would be very appreciated. Thanks