Let me try! I'll shoot for not too much info, and not too little. Yes, a relay takes a small input signal, lets say from a switch on the dash, and turns that signal into a closed circuit for a device that is a higher current consumer, say for example a headlight or a horn. The reason they came to be was to prevent running the higher gauge wires that the electrical comsumers need all the way to the switch. In the case of something a little more complex, say the example of a fuel pump relay, the main job is the same, turning on and off the fuel pump, but instead of a switch that the driver operates, there are many switches that decide that it is OK for the fuel pump to run, and none of them are really controlled by the driver, except in a very remote sense (turning the key on and off).....Gilly