The first thing you need to do is disconnect your car battery. Make sure your stereo doesn’t have any security features that might disable it if the power is cut, as some do require unlock codes. First, disconnect the negative terminal, then disconnect the positive terminal. You must do them in that order. Be very careful and try not to lean directly over the battery, as they can in rare cases actually explode.
Now you need to run the power cable. This cable connects the positive terminal of the battery directly to the amplifier, and it should have an in-line fuse to help protect the amp from power issues. This fuse should be removed before you connect the wires. What the fuse does is bridge the connection with the cables, so the other end of the power cable won’t be hot when you connect it to the amp.
The most difficult part of this whole process, in my opinion, is running the power cable because you have to go from the engine compartment to somewhere in the interior of the vehicle. I usually run my cables through the rubber gasket that allows all the other wires and cables to go through the dash to the engine compartment. If you look somewhere near the steering column, you should find a place to run the power cable and I don’t recommend drilling unless you absolutely have no other choice. Very carefully poke a small hole in that rubber gasket and feed the cable through.
You will need to snake the power cable under the dash and to wherever you have the amp, which is typically in the back of the car. If you have a center console in your vehicle, you can hide the cable under it. Just be very careful under your dash that you don’t obstruct your pedals or any other mechanical devices in any way. You may want to keep a few small zip ties on hand to secure the cable.