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How to use DMM to diagnose Headlight wiring issues?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by wlai, Mar 25, 2024.

  1. wlai

    wlai Junior Member

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    I've been having a devil of a time with an intermittent headlight issue on a 2008 Touring with HID. The stages of "grief" has been:

    - Passenger headlight bulb goes on and off randomly
    - A bulb change on the passenger side didn't fix it...
    - So I just went ahead and replaced both ballasts and both bulbs, which also involves disassembling both headlight assemblies and clearing out some condensation, etc.
    - Now Passenger headlight is consistently working, but Driver side headlight is intermittent, to outright dead
    - Swaped the bulb on the Driver side and that didn't do the trick

    Now I'm wondering if I had swapped some wiring by mistake and transferred the gremlin to the driver side. Since there are only three wiring cords that comes from car to the headlight (as opposed to the other two that controls the turn signal and the parking light), is there a technical ref on what are the expected voltage levels coming out of those three wiring, so I can double check it's not an issue from the wiring harness outside of the headlight assembly?
     
    #1 wlai, Mar 25, 2024
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Official wiring diagrams & more.

    There are unofficial (free) ones circulating the internet as well.

    It may help to understand behavior: HID lamps do a self-test when they are first powered up. If they think they have a problem, they are required to self-extinguish to prevent blinding glare. That's a regulatory requirement for all HIDs, not just something Toyota did.

    So by 'intermittent' you may be seeing the thing try to light up, fail the self-test and then go into protective shut-down mode.

    The link above will include directions to the repair manual which has Toyota's real step-by-step procedure for fully troubleshooting the headlight system.
     
    #2 Leadfoot J. McCoalroller, Mar 25, 2024
    wlai likes this.
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Just editorial: DMM = Digital Multi Meter??
     
    #3 Mendel Leisk, Mar 25, 2024
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    #4 mr_guy_mann, Mar 25, 2024
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    Definitely get yourself a copy of the factory service manual.

    The 2 wire connector that's on the twist-lock bulb access cover should have "12V" battery power and ground when the headlights are on. I have had corrosion problems with that connector.

    From there the wires go right to the ballast.

    High beam on a HID light is just an "eyebrow" shutter controlled by a solenoid. The switch triggers the solenoids and move the shutters, allowing more light to shine out.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, Mar 25, 2024
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  6. PriusCamper

    PriusCamper Senior Member

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    These HID systems are awful... By a new set of headlight cases online for $150 that hold Halogen or LED bulbs and wire those dumb ballasts out of the system entirely. It's not worth continuing the hassle you're going through.
     
    #6 PriusCamper, Mar 25, 2024
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  7. wlai

    wlai Junior Member

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    PriusCamper, do the new non-HID housings contain the necessary wiring? Where would I get those?
     
    #7 wlai, Mar 31, 2024
  8. PriusCamper

    PriusCamper Senior Member

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    You have to rewire it... It's pretty simple... You just buy these headlight plugs: http://www.amazon.com/Dorman-84790-Headlight-Socket/dp/B001SGBZSQ Then you find the correct high beam wire, low beam wire and ground wires in your existing wiring and connect them.
     
    #8 PriusCamper, Mar 31, 2024
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