At first I thought something was missing. Wasn't there an air cartridge? I finally figured out that you just screw the air hose into the tire valve. So simple and easy. I have a new Jeep Wrangler 2 door. I deflated some air from the rear spare tire and attached the wires to the battery which is easily accessible in the jeep. He started the jeep, set the necessary units and pressure, but nothing happened. The compressor did not turn on. Then I found that the power switch on the bottom of the device was off. Plugged it in and it started inflating my tire from 35psi to 40psi in less than a minute. At lower pressure, of course, it runs much faster. The whole process is simple and straightforward. I am very happy. I wanted to test it before I really need it. Now I'm sure. This makes it easier to inflate and secure for off-road and street riding and check tire pressure for maintenance. They say don't try to just use the cigarette lighter, connect it directly to the battery and start the engine. The auxiliary output has a 20A fuse, the compressor runs at 25A and the fuse may blow. Follow the instructions and avoid problems. Even for us half-blind seniors, the digital display is easy to read.