Switching 12V vehicle headlights with Arduino / Mosfet combination

Thread Starter


Joined Mar 25, 2021
Quick intro: a ground level noob, started to tinker with electronics at the beginning of this year after I couldn't get any electronics shop in my town replace my bike's gauge cluster SMD LEDs. I bought a trash soldering iron and looked at few tutorials and did the job myself - surprisingly it worked, but I bought too bright SMD's and I didn't like the temperature of the color, so I thought about if there's a way to have it adjustable at all times.

I discovered addressable leds, drivers, ESP32's and all that, and eventually installed the addressable LEDs in the cluster, controlled wirelessly via phone app, and now I'm looking to make a new project.

I learned few things about mosfets, I managed to assemble a code for Arduino IDE that controls the LED the way I want, and tested the 12V 25W LED bulb on my desk with bench power supply and Arduino hooked to buck converter, with the LED bulb controlled with a breadboard size pushbutton and a mosfet. I bought the wrong (high Rds, not logic level) nMOS at first, but learned to read some specs and got IRL2203 that operates the light and keeps cool with no heatsink.

The challenge is how to install it in the vehicle while keeping the original controls intact and without adding anything extra. I am going thru YouTube vids on schematics and trying to figure out where in the "headlight circuit" should I tap in with the Arduino and mosfet. One thing that kind of worries me now, I'm starting to think I planned this wrong going with the nMOS and all, I highlighted all the headlight-relay wires and it seems that pMOS would be the correct choice to tap into these wires, and accessing ground wires for nMOS would be too challenging?

As I'm not well versed in these, please let me know what can I do here.

One idea I had was completely remove headlights from the circuit, from the relay and everything, and run a separate circuit from headlight fuse? Just thinking out loud :D Let me know how would I go about solving this :) cheers



Joined Sep 9, 2010
The challenge is how to install it in the vehicle while keeping the original controls intact and without adding anything extra.
So help me understand the goal. It sounds like your device is something you adjust once and never touch again. You want to install it so that the bike's original functions are retained, but the new lighting system is additionally modified by the device?


Joined Jan 27, 2019
I can't quite tell what you are trying to do but I wonder about the idea of interfacing the existing controls to the Arduino and using the existing relay. Or, adding the Arduino as an additional control, but to control the relay, not the headlight.