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Footwell lights always dim

Discussion in 'Prime Main Forum (2017-2022)' started by Sezy, Jul 6, 2020.

  1. Sezy

    Sezy Active Member

    Joined:
    Oct 19, 2013
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    Location:
    Saint Charles, Missouri
    Vehicle:
    2020 Prius Prime
    Model:
    Limited
    The factory footwell lights on both sides in my 2020 Prime Limited used to light up bright when the door opened then dim while shifting into gear. 7.5 Amp Fuse is good, has been replaced & the dome lights work as expected on the same circuit. Unplugged the negative battery overnight, no change. Voltage on the light is odd as both wires are positive. Measured together i get 2.8 volts. One side of the wire to a ground is 12 volts the other to a ground is 9 volts. Tried adding my own ground to the 9v side & the brightness I expected came back but the light would stay on past the dome light timeout. Stared 2 weeks ago. Unplugged every LED bulb I put in, disconnected my hardwire dash cam. Even though my dash cam wiring does not touch the lights the dealer wouldn't touch it under warranty blaming my wiring aka fuse tap to the power outlet. Hooked car up to Techsteam, ran through all lighting test. Turning the fog lights, door lights anything on then off from a computer click but the footwell lights did nothing when told to turn off via Techstream.

    Any guesses? Willing to try a different dome light cutoff relay if I can find where it is.

    20200630_184419.jpeg

    Posted via the PriusChat mobile app.
     
    #1 Sezy, Jul 6, 2020
  2. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    11,491
    14,100
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    Location:
    Tampa, FL
    Vehicle:
    2017 Prius
    Model:
    Two
    My guess is that there's something amiss with the wiring mods you made and it's somehow back feeding the footwell lights with some other load in series with them. Putting the ground on the low side gives the needed 12v drop across the lights, but since many automotive switches are on the ground rather than the hot, the lights don't turn off. I can't think of any way to troubleshoot it without physically following the wires. Automotive wiring is weird.
     
    #2 jerrymildred, Jul 8, 2020
  3. pghyndman

    pghyndman Active Member

    Joined:
    Dec 27, 2018
    498
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    0
    Location:
    CT shoreline
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    FWIW: One of my cars requires a ballast resistor whenever a low current draw LED is used in lieu of an incandescent lamp... (heck, sometimes even if a non-compliant incandescent is used), lest the computer (Signal Acquisition Modules etc) go nuts (translation: all sorts of crazy, seemingly unrelated uh-ohs can crop up when one attempts to (ahem!) re-engineer a system. I've spent too much time chasing my tail from self-induced problems.

    Just sayin' :)
     
    #3 pghyndman, Jul 9, 2020
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