February 3, 2023
How To Wire An Automotive Relay In 5 Steps?

Automotive relays are small switches that can control electrical circuits or components in vehicles. A relay consists of three main parts: the coil, the switch, and the contacts. To understand how to wire an automotive relay, you must first understand how these parts work together to perform the relay’s switching function. To learn more about automotive relays, read below!


Make sure you are using the right relay for your application. *The number of the coil and load contacts will match the wiring diagram on the back of the relay. Choose a single or double throw, depending on what type of switching you want it to do. *You’ll also need wires, terminals, a switch and some insulation tape.
*To begin with, solder one lead from each coil contacts to a separate wire stripped at both ends.

Connect The Battery And Start Wiring

Connect the battery and then strip and cut a couple of inches off the ends of each wire. Put them together, connect one end to the positive terminal on the battery, and crimp on a butt connector. Connect the other end of each wire together so they’ll all have power. Twist them tightly with some electrical tape, so they don’t come apart while you’re working with them or inside the car’s engine bay.

Move both batteries as far away from one another as possible – If you can lay them flat or place them vertically against a wall that’s not in use, do it. The point is to keep the wires from grounding against one another and shorting out because that can fry your device.

Add Additional Wires

1. Route all wires from the harness connector labelled two and wired them into the box labelled two on the second row of pinouts at the front of the relay bank.
2. Route all wires from the harness connector labelled three and wired them into box three on the second row of pinouts at the front of the relay bank, closest to column 4 of relays in slot 12.
3. Make sure no other wires cross over other sets of pins when inserting your jumper. Insert one end into box 3 (the only hole available) and press firmly with a pen or other object until it clicks and is held securely inside of the relay bank.

Add A Switch

Now that you have a fully functioning wiring diagram, you can use it to make your relay work. You’ll need to attach a wire from the Ground terminal on the coil connector (labelled as Rc or L1) back to one of the screws you used for safety purposes before connecting any wires between the terminals. One side of this wire will connect with the screw, and the other side will be left bare.

Please make sure these connections are tight, so they don’t come undone during use. Next, attach two wires from another terminal of the coil connector- one black and one red-to opposite poles on your switch. Finally, take the black wire attached at Step 3 and attach it with tape or a solder joint to where that end was joined at Step 1.

 Test And Adjust

Attach the male end of a jumper wire to one terminal and a female connector. You can also use alligator clips if you don’t have a connector.
Attach the female end of a jumper wire to the other terminal and attach it to the car’s battery or power supply. The jumper wires should be about three feet long for safety reasons. If possible, get someone else to do this step for you.
Observe your car; does it start? If not, make adjustments until it does. For example, replace the positive side with a new battery or adjust the voltage setting on your electrical supply if necessary


Congratulations! You’ve learned how to wire a relay and now have the necessary know-how to install a relay on your car. Keep the wiring diagram as a reference and use it whenever you need help troubleshooting your installation. Your ignition switch should be within reach of one of the wires attached to the relay.

Once you are ready, plug the battery back in, open and close the door, hit the unlock button on your key fob (or pull up on the trunk latch) and test out your new upgrade by turning your headlights off using just 10 seconds of power from a dime store battery.

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