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Wiring Diagram for Front Headlights: How to Connect a Relay

Model: (Various brands) Various
Part: Headlight

Video tutorial

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


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