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Needing to find a switched 12V fuse under the hood

Discussion in 'Gen 2 Prius Main Forum' started by ColoradoCrow, Jul 17, 2024.

  1. ColoradoCrow

    ColoradoCrow Active Member

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    Hi all. I installed fog lights and need to tap into the 12V power supply under the hood at the fuse box. All the fuses I have metered are 12Volt all the time which makes sense. The trouble is I’m running an illuminated rocker switch for the fog lights which will drain the battery. I have found a switched wire inside the car but I need to find one under the hood. any ideas?
     
    #1 ColoradoCrow, Jul 17, 2024
  2. ColoradoCrow

    ColoradoCrow Active Member

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    Good morning. It would make sense that the fuses have constant 12volt on both sides of the switch as I’m looking for a source after the ignition switch. I even tried the fog light 7.5 fuse which is labeled on the fuse box to no avail. I’m trying to avoid having to run another wire through the firewall but Inthink I am going to have to do this. Any thoughts?
     
    #2 ColoradoCrow, Jul 18, 2024
  3. BiomedO1

    BiomedO1 Senior Member

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    Put a relay under the hood. Fused and constant hot on one side of relay. The existing wire going through the firewall becomes a switching wire to turn the relay on-off. Power tap into an accessory switched wire under the dash to your illuminated switch, that way when ignition is off you lose power to the switch and the fogs goes off automatically. You won't be able to power the fogs without turning-on the car.

    Good Luck....
     
    #3 BiomedO1, Jul 18, 2024
    ColoradoCrow likes this.
  4. ColoradoCrow

    ColoradoCrow Active Member

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    Thanks. It is a Nilight wiring harness for 16awg 2 fog light kit. There is a relay. But I agree with having it connect to switches power. I will have to run a second wire from the power to a switched power wire behind the radio. It seems. I’ll take the dash apart again to locate one
     
    #4 ColoradoCrow, Jul 18, 2024
  5. rjparker

    rjparker Tu Humilde Sirviente

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    The IG2 ignition relay is in the engine fuse box as part of a module called Unit B. You could tap its output under the fuse box to drive a relay. The same relay feeds 12v to the coils and other devices on the engine.

    IMG_5686.jpeg
    Prius Gen2 Eng Fuse Box & Fusible Link Mechanical.jpeg
     
    #5 rjparker, Jul 18, 2024
  6. ColoradoCrow

    ColoradoCrow Active Member

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    TY RJ THIS WORKED OUT GREAT. I added a tap to one of the empty slots under Unit B and now have switched power for the fog lights.
    I will upload photos shortly. I have pics of the rocker switch and the Lights themselves. This will help out night driving in the winter for sure.
     
    #6 ColoradoCrow, Jul 20, 2024
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