A preamp is used to improve the sound quality and power of your car stereo. It can increase the voltage to your system, add equalization and improve other areas of performance depending on which one you choose and how you set up the system. Generally, the preamp is installed with the amp to boost the level of output of the entire system. It is where you will plug in the electronics of the system, so it is also like a switch port.
The installation of a preamp involves basic connections to the preamp and power amp, which supplies the power current for the stereo. Your preamp will have instructions and wiring diagrams detailing how these connections should be made. Each preamp is different. Some receive power, others are passive and receive no power. Still more will have connections from other components that need to be installed as well. Each one will have a different type of installation.
Placement in Your System
To set up the preamp for installation the first step is to find a spot for it in your car. Usually this is near the amp, but if your amp runs very hot you may want to set it a few feet away. The preamp can be installed in the trunk as long as you can find wiring for each component that the preamp will host. Most electronics stores sell wiring kits for preamps and amplifiers that are 20 feet long, so this should not be a concern.