car wire fire the 12v source
12 Volt Housings

12 volt
car stereo
car security



12 Volts


A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts. When an electric current is passed through the coil it generates a magnetic field that attracts the armature, and the consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open.


30/40 Amp Single Pole Double Throw Relay



The relay acts like a "switch" when the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position.. A relays reaction is almost immediate. and can be triggered with an electrical pulse minumum of 150 milliamps and switched output of 30 to 40 amps. In a low-voltage application this reduces noise and in a high voltage it reduces arcing. The relay is an essential component in car audio and car security installations.


S.P.D.T Relay Footprint

The single pole double throw relay will consists of five prongs.




Relay at Rest

A relay unenergized will rest at normally closed 87a



30 Common

87a Normally Closed

87 Normally Open

85 Ground

86 12V


Relay Energized

Once the relay is energized the armature is repositioned to 87.



In many cases, the connection of pins 85 and 86 can be interchangeable, but NOT if there is a diode wired across the coil.













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