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Fog light debug

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  • Fog light debug

    Electrical is not my strongest asset. Trying to get my fogs going. Installed two new lenses and H3 bulbs in my 88 with no luck.

    Here's what I have so far:
    2 new lenses
    2 new H3 bulbs
    Harnesses look good and cleaned with contact cleaner
    Dash switch removed
    Off - no continuity between any pins
    On - continuity between pins 2&4, 2&6, 4&6. Nothing at pin 8

    Both fuses are good and measure 0 volts/amps with headlights and fogs on.

    Any help where to start would be appreciated.

  • #2
    For the fog lights to "come on" a few things need to happen. The light switch must be in "low beam position and the fog light switch must be "on". This energizes the K8 Fog Light Relay .If K8 is energized and fuses 29 and 30 are OK, the fog light will be on as well as the instrument cluster indicator.

    good luck


    • #3
      I am currently working through a similar problem in my MTech Cabrio.
      A few things you can try that I have done to get to the point where I am in my process. I got side tracked and have not pursued it in a few months...

      1) Remove the fog light relay and make a male to male blade jumper.
      Jump the 12v supply relay pin to each respective fog light pin.
      If the lights come on your problem is on the control side.
      If they don't come on its probably on the output side..

      If I remember right the fog light switch provides the relays ground to turn the lights on..
      Next check continuity between the switch s ground pin and ground

      Then check continuity between that ground pin on the relay port in the fuse box and the corresponding pin on the fog light switch connector.

      Thats where mine is failed.
      I can make both fog lights come on by jumping the always hot supply pin to each light.
      My switch establishes continuity to ground when pressed.
      What I think is wrong with mine is the connection on the other side of the switch to the activation port in the fuse box.

      Hope that helps some.
      Sorry I don't have my ETM in front of me otherwise I could speak in wire colors and pin numbers.

      Last edited by jimmy p.; 10-26-2017, 02:24 PM.
      jimmy p.
      87 E30 M3 Prodrive British Touring Car
      88 E30 M3 Zinnoberot - Street
      88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
      92 E30 M Technic Cabrio - S14 POWERED!
      98 318Ti M44, Base - Morea Green
      04 Ford F350 - V10


      • #4
        Check your grounds. My fog light on my drivers side has an issue in the ground. The harness is beautiful, but somewhere there is an issue with the ground. I wired a new ground wire in and they worked fine.

        '69 Datsun 2000 Roadster vintage race car (Street driven on a regular basis :taz
        '59 Alfa Romeo 101 Sprint (HUGE project :uhoh
        '88 M3


        • #5
          I pulled and tested relay K8 this morning. No continuity or resistance between any of the pins. In a typical 4 pin relay, pins 86/87 should have continuity and resistance. With 12+ to 86 and 12V- to 85 no click. I'm going to order a new relay in the morning.

          My bigger fear is what killed the relay...


          • #6
            I changed the relay, still no fogs.

            The dash switch out
            Off - No continuity between any pins
            On - Continuity between pins 2&4, 2&6, 4&6. Nothing at pin 8.

            Is is this correct?


            • #7
              Front fog lights require the head lights to be switched on be it as park/driving lights (pull knob till 1st notch) or as dipped beam (knob pulled fully). Only then pressing the button for the front fog lights will actually switch them on


              • #8
                I had the same problem. I finally tested my new relay and found it to be bad. I tested my switch, relay, fog lights lights and it was the new relay. BTW I found my fog lights did not have bulbs in them when they were shipped to me. Also make sure your wiring is not cut along the way.


                • #9
                  Make sure to use BOSCH relays. I was chasing down a no start issue on my e23 745i for about a week until my old man randomly visited and made a comment on using non bosch. "Use bosch. napa relays wont work right. We had a lot of issues like this in the old days" . Sure enough that did the trick (main relay)
                  sigpic 95 M3 & 88 M3