Most people just do that thing where you pull the handle to you and your “brights” come on.

Not trying to be a dick, but I’ve met a few people who grew up in cities and legitimately didn’t know “brights” were a thing

But in any case, dont fuck with your headlights, they’re an important safety feature.

So a few things…

• Some LEDs are not ‘dimmable’ – which means they turn on once the voltage hits a certain level, and off if it falls below another level. For low/high beams, a lot of cars use two separate bulbs, angled differently. To make it dimmmable, you’ll need automotive-grade bulbs that can work across a range of voltages and/or currents.

• Most cars are now based on digital control units that communicate via CAN busses. When you press the window down button, it’s sending an on/off signal to the window controller, which runs code that turns on the window motor. Another sensor sends back the level of the window so the controller keeps the motor running until it’s reached a certain level. This is how you can tap the window lower button and it continues lowering the window even if the button isn’t pressed.

• If you patch into the bulb at the wrong place, your potentiometer may drop the voltage down to a level that the headlight controller might think it’s malfunctioning and signal it as a busted lamp. It may also void your warranty or cause issues with repair down the line.

• If the potentiometer and regular headlight switch state are not synced, they headlight controller could think it’s on, but maybe it’s not. So it could become a safety hazard issue.

• The circuit to manage the potentiometer will need its own power. If you ‘borrow’ power from the car battery, it may continue drawing even when the car is turned off. This could drain your battery. When you press the button to turn ‘off’ the car, it sends a signal to the main sytem controller which sends a bunch of signals to the other sub-controllers to change state (turn off display panel, engine, transmission, stereo, AC, headlights, etc). Your lamp will not be known to the controller, so it won’t know to turn it off.

• Two ways to try what you want. a) read up on the car’s CAN messages. They’re likely proprietary, but a lot of models have been reverse engineered. There’s a chance the light controller already supports dimming, but you only have two switches (on/off, low/high) in the cabin. If you send it the right CANBus message, it may do the dimming for you. b) Second way is to leave the regular headlamps alone and install a third-party headlamp (like the ones people put on top of their jeep rollbars), and just wire a separate dimmer to that.

• To get access to the CANBus you can either go directly under the hood and patch it in, or get a little OBD2 dongle that plugs into a socket under the steering wheel. They sell these cheap dongles with bluetooth so you can monitor and control settings via a mobile phone app.

• Be aware, however, that OBD2 gives you access to only a subset of the control commands. Also, on some model cars, the raw CANBus messages are encrypted so you may want to do some research on which devices work with your specific model, what the CAN message codes are, etc.

Best of luck. HTH.

LEDs have a driving circuit to them, putting a potentiometer in there will just under power the driver and probably do nothing to the LEDs brightness at all. In order to dim LEDs, a driving circuit turns them on and off really fast with a PWM signal, not variable voltage. I’d recommend trying to build a LED driving circuit with an Arduino to get a mechanical understanding of how they work, then never touching your headlights. Proper headlights are lensed so they can be bright but not shine into people’s eyes. If your Prius does not have LED lights from factory, but you want brighter lights, just replace your current halogens with higher quality/brighter halogens rather than poorly implemented import LED bulbs that’ll rarely work right in halogen reflectors and cause you to be an on road nuisance. You are probably also due for a headlight polishing, which you can buy a kit for, and will significantly improve your headlight brightness.

If you’re in the USA I believe that there is no street legal LED light conversion kit, unless you buy the OE parts and swap them out.

Which is to say you’re gonna be driving around with ultra bright “I’m an asshole” lights if you do this.

Don’t do this.

LED lights are either off or on, you can’t dim them. They run off of 5v. Less then that, they don’t light, more than that, you will burn them out