Basic Relay Information and Function

The purpose of a relay is to be able to use a switched, low amp circuit to operate a high amp draw component. We are discussing using a relay with an electric cooling fan but a relay is used in many circuits in your car such as fog lights, power windows or seats, horn, etc.

A cooling fan, or any of the other accessories listed, can draw 15,20,30 amps or more - a basic toggle, window or light switch are not designed to handle that much amperage through it without overheating the switch and eventually damaging the switch and could even cause an electrical fire. A "switch" can be one you operate with your finger or it can be operated by engine coolant temp, oil pressure or AC system pressure - no matter what/how a switch is activated, it is still just a switch that either turns something on or off.