Relay: How It work and the differences

SPDT relays are widely use in automobile. I have found a few type of relay for different of application. But How does relay work?

Relay work when power apply to terminal 85 and 86. This will result the coil energized and create a magnetic field.
Normal state before power apply to relay is terminal 30 connected to terminal 87a also known as normally close state.
After coil energized, magnetic field will attract terminal 30 spade from terminal 87a moving toward terminal 87. Therefore, power from terminal 30 will transfer to terminal 87.

So far, I found 3 type of it.

• Normal relay or horn relay
• Immobiliser relay
• Power Window relay

   Here is the internal picture of the relays.

For the power window relay, terminal 87 and 87a are internally connected. So when coil energized, both terminal will have powered.

For the immobilizer relay, it dont have pin 87. Which mean this relay only have normally close state. When alarm or immobilizer triggered, it will activated relay and therefore with proper wiring engine cannot start.