Do it yourself
Frequently asked questions about cars and motorcycles
Car tutorial (Do it yourself) Motorcycle tutorial (Do it yourself) Frequently Asked Questions

Wiring Diagram for Front Headlights: How to Connect a Relay

Model: (Various brands) Various
Part: Headlight

Video tutorial
Detailed instructions - The aim of the video is to use the relay to pass direct current from the battery to the headlight bulbs, using the original switch only as a "command" to activate the relay. This improves efficiency and brightness. A standard relay usually has 5 pins (like the one in the video) connected as follows: PIN 30 (Power IN) connect this PIN via a 15/20A fuse for each headlight, directly to the positive terminal of the battery. This will power the headlights. PIN 87 (Power OUT) connect this PIN to the positive wires of the front headlights. Usually, the original positive wire going to the headlights is cut and connected to this PIN. PIN 86 (command+) connect this PIN to the control source. This will be the wire that provides +12V when the switch turns on the headlights; it can be the positive wire for the dipped beam or main beam, depending on what you want to control. PIN 85 (command-/ground) connect this PIN to a good, clean chassis ground. The 5th PIN 87a is not used in this diagram.

Posted on 17 April 2026 by ScegliAuto


Related tutorials

How to read the electrical diagram of a starter relay
(Various brands) Various In this drawing we see a standard 4-pin relay, marked with numbers: 30 is the power supply directly from the battery; 85 and 86 are the control coil,…
Removing Front Headlight Bulbs
Removing Front Headlight Bulbs
(Various brands) Various Learn how to remove the front headlight bulbs of your car. Lift the front bonnet to access the rear of the headlight. Remove the plastic cover (at th…
Electrical Connection for Tow Bar
Electrical Connection for Tow Bar
(Various brands) Various In this video, we will see how to install a tow bar for the car, describing the mechanical part, which involves (and varies depending on the model of…

Other guides you may be interested in

How to Adjust the Handbrake on a BMW 1 Series?

To adjust the handbrake on a BMW 1 Series, use a tool to pry off the leather cover that wraps around the base of the handbrake lever. Once this cover is removed, you will be able to locate the spring that regulates the handbrake tension. At this point, adjust the nut located at the base of the spring: tightening the nut will make the handbrake firmer and reduce the lever's travel. Conversely, loosening the nut will decrease the handbrake's firmness and increase the lever's travel.

Watch the video!


by ScegliAuto

More videos