Invest in some of these, one of these, some self tapping screws, and some ring terminals.
Since your later comment says you've had it this way for 7 months, you need to know this kind of laziness is bound to cause problems. Problems such as blown fuses, intermittent operation, noise heard from the speakers, and possibly a fire. Do you know how it feels to have your car start on fire due to an electrical fault? I do, and it's the worst feeling.