How to add a light which turns on with DRL or headlights?

Discussion in 'Gen 4 Prius Technical Discussion' started by PAW, Jan 16, 2026.

  1. PAW

    PAW New Member

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    2022 Prius
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    I have a 2022 Prius LE.
    I want to add an LED light which would come on when the DRL/headlight is turned on. Otherwise it should remain off.
    (for discussion let's ignore the new light's amps/watts).

    Do you have ideas of how to do this?

    I am able to tap into the DRL and headlight wiring to get power for the new light when they are turned on, but I'm pretty sure wiring the DRL and headlights together to the new light will cause "bad things to happen."

    I read somewhere about the idea of using a relay so only one source can connect power to the new light. I like the concept but I have no experience or knowledge of automotive relays.

    Any suggestions appreciated.
     
  2. PAW

    PAW New Member

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    Update
    I can't figure out how to turn the light on "automatically" via relays.
    My dashboard has no empty places for a switch.
    I will repurpose the otherwise-unused HUD button on the multi-function switch. That goes to an MGI fused relay connected to switched power to turn the light on/off.
    If I ever figure out an "automatic" approach I can disconnect the switch & change the relays.
     
  3. AzWxGuy

    AzWxGuy Weather Guy

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    Your vehicle might already have an indicator light for DRL/headlight. In the plethora of indicators in the annunciator panel (far right third of the dashboard) there is a headlight indicator. There may be slight differences between model years and vehicle options, so I'm not certain about this feature for your model year. My Owners Manual pg.110 has the symbol and a reference page to read about it.

    upload_2026-2-7_5-11-17.png

    Something else I discovered the other day. If my vehicle is made ready, in Park, with headlights set to Auto (DRL enabled) and I engage the emergency brake, the DRL and dashboard indicator light extinguish. Maybe that is how I can have what used to be called parking lights.
     

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  4. VelvetFoot

    VelvetFoot Active Member

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    Gen5 LE owner here. Learning as well.

    My LE does not have auto on/off headlights.
    I liked them in my last car

    There is no indicator for when the drls are on.
    It's, like, 3 rotational steps on the stalk.
    I've left the drls on when I didn't want to.

    Of course, I've driven sans headlights until getting 'flashed' by on-coming drivers, so there's that.
     
  5. BiomedO1

    BiomedO1 Senior Member

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    I don't see what's so difficult??? I do this all the time and even chained relays together to form an if-and-or-circuit. If you can't figure it out; you should probably pay someone, before you "fry" your electrical system.
    - YouTube