By - Vince Galti (VinVin)
Relays are one of the most useful components in a car electrical system. They allow you to do many simple and complicated tasks, both efficiently and safely. At first you might think relays are complicated to use, but with practice and an understand of how they actually work, It becomes clear just how easy they are to use.
Some common tasks a relay might perform are:
- Supplying power to extra driving lights (fog lights) or neon’s etc.
- Boosting the strength of the remote wire from your Head Unit to run multiple amps, electric antenna or interior neon’s etc.
- Changing positive signals to negative signals (Alarms)
- Sending a +’ive signal to a wire that rests on ground (so it doesn’t short out)
- A Solenoid
- A two way switch
Pin 85 and 86 are the solenoid pins. This is what controls the relay. If you connect pin 85 to earth, and pin 86 to 12v+, then the solenoid will activate, making a click sound. When you disconnect one of the pins, the relay will click again as the solenoid returns to normal.
What is the click?
When the solenoid is powered up, it creates a magnetic field, which moves the two way switch inside.
In normal position (no power to pins 85/86) the switch is set in position 30 – 87A. This means there is a dead short from pin 30 to 87A. When the solenoid is activated (click) the switch moves from 87A to 87, and then back when the solenoid is de-activated.
A more simple way to look at it is the relay is one switch controlling another.
How can we put this to use now?
Example: Wiring up fog lights in a car that will work when the park lights are on.
Pin 85: This goes to the wire which gets +’ve power when the park lights are on (often found in the lume running up the steering column).
Pin 86: Because pin 85 has +’ve when on, we need an Earth on pin 86 to activate the relay.
Pin 30: Connect this to the power source for the Fog lights, note that it is a FUSED wire. This is the wire which will be supplying to power to run the Fog Lights. Best place to pick it up is at the battery under the bonnet, and fuse it close by.
Pin 87: +’ve power output to the fog lights.
So, when the park lights are turned on, the solenoid activates and connects pin 30 to pin 87, causing power to run to the fog lights.
Example: Running multiple amps and cooling fans off the remote wire from the Stereo.
Pin 85: +’ve output on HU remote wire.
Pin 86: Earth, to activate solenoid when HU is turned on.
Pin 30: Fused +’ve power
Pin 87: +’ve power output to run multiple amps and fans etc.