A Nissan power window relay allows the windows to function, even when the engine is turned off, and the key is not in the ignition. Typically, power windows, as well as all other electronic devices in a car, can only function with the engine turned on. During operation, they draw their energy from the alternator. When the car is not running, these devices draw their energy from the car's battery. When the key is not in the ignition, it is impossible to use the power windows at all, without a relay.
Prior to 2004, Nissan used a device in their window circuit called a "smart entrance control unit", which controlled the master switch of the vehicle's power window circuit. The master switch in the car controlled the operation of all windows, and had its own central processing unit. The smart entrance control unit utilized a power relay, which provided power to each of the power switches. From 2004 and onward, the smart entrance control unit was renamed as "body computer module". The body computer module no longer contained a power relay.
The relay contains an electromagnet to provide the initial power. Electromagnets are temporary magnets, they are only magnetic when electric current is flowing through them. When electric current flows through the wire inside an electromagnet, it creates a magnetic field, which can store power. The electromagnet in a Nissan power window relay stores a small amount of power, just enough to switch on an armature, which holds 12 Volts of power. The magnetic field attracts the armature, which provides the additional power needed to activate the window.
The power window relay is not meant for extensive use. Power window relays are a convenience, intended to be used sparingly. If used too extensively, the armature will exhaust its power, and the window will no longer function until the key is in the ignition once more.
