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Have you ever been tempted to put LEDs in the dash?

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  • Have you ever been tempted to put LEDs in the dash?

    Well, get that stupid idea out of your head!

    During the winter when the car was stuck in the garage I got that itch to do something to it so I decided to replace all dash lights with LEDs.

    I took my car out last week and discovered 2 important problems.
    1. The engine now needs to be revved higher to engage the alternator, probably the battery bulb resistance somehow plays an important part in this.

    2. When the car idles, apparently some current flows through the battery bulb. With the regular bulb this current is so small that the bulb looks off. But with LEDs it's enough to make it glow a little, which is very annoying.

    So in an effort to save time and avoid disappointment I am letting you know.

    Tonight I have to take the dash apart again.... what a PITA.



    - Tire is the other control arm bushing.

    zhpregistry.net

  • #2
    Did you just install LED's in place of the warning/information lights, or did you replace all the cluster lights as well?
    Chris L.

    Spray paint and tire shine doesn't equate to a "restoration!"

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    • #3
      never occurred to me


      that being said, what exact LED's did you use? as you are finding out, LED's are very different than incandescent bulbs. it sounds like you have the anode's and cathode's hooked up correctly
      James
      sigpic

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      • #4
        Originally posted by UNHCLL View Post
        Did you just install LED's in place of the warning/information lights, or did you replace all the cluster lights as well?
        Yes, just replaced the blinker indicator, high beam, and all the ones in the lower right corner (ABS, Handbrake, Battery, oil etc.)



        - Tire is the other control arm bushing.

        zhpregistry.net

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        • #5
          You can't replace the alternator bulb with a standard LED. An LED is a diode, which only allows current to flow in one direction. When you turn the key to the on position, 12V flows through the bulb from the switch, and is grounded inside the alternator. This 12V also 'excites' the alt. After the engine starts, the alt supplies 12V to the bulb wire, so the light goes out.(12v on each side of the bulb = no current flow). When you installed the led, you also had to install a resistor to limit the current thru the led, so the 12v never reaches the alt from the ign switch, so it does't get 'excited'. When the engine is revved to a certain RPM, the alt 'self-excites', this is so if the bulb burns out you won't kill the battery.
          Just replace the alt led back to the bulb, the LED's on the other cicuits will not cause any problems
          If your incandescent bulb is glowing slightly, either your alt is going bad, or you have an excessive voltage drop somewhere in the system - bad ground, corroded connection, etc., etc. (The voltage is higher on one side of the bulb than the other)

          jimmyC

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          • #6
            Good post Jimmy. Using incandescent bulbs the light glows so little that if there is any ambient light (street lights) I can't see it. Only in a complete pitch dark environment like locked in a garage with all the lights off I may see a slight hint of a glow. I personally don't think it's a problem... do you?



            - Tire is the other control arm bushing.

            zhpregistry.net

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            • #7
              Well, not if it's that bright.

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              • #8
                so it's not a good idea replacing the 2821 3watt bulb(orange glow) with led's??

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                • #9
                  Jimmy always has great posts regarding circuitry/electronics. Very easy for the reader to digest.:chug:

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                  • #10
                    I was told that the "rev car to start the alternator" was a common M3 quirk.

                    If I release my handbrake, my dash lights turn off and it starts the alt. just like when I blip the throttle. I have always wished for an easy fix to this.
                    Steve
                    "Technology is the only replacement for displacement" - TRD

                    (For business related questions please contact my other user name '[email protected]')

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                    • #11
                      I did not exactly replace the stock light with LEDs, but I installed warning lights for oil pressure, fuel pressue, and coolant temp using super-bright 10mm LEDs. They are wired to aftermarket (SPA) gauges, not the stock warning circuits. I did this because while driving "aggressively", there is no way I would ever notice the stock lights should they go on. The 10mm LEDs will be noticed, even in bright sunlight.

                      At any rate, I have had no problems with this setup. They go on when they should and stay off the rest of the time.....

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                      • #12
                        Originally posted by Sbailey294 View Post
                        I was told that the "rev car to start the alternator" was a common M3 quirk.

                        If I release my handbrake, my dash lights turn off and it starts the alt. just like when I blip the throttle. I have always wished for an easy fix to this.
                        Perhaps this should be posted elsewhere, but on occasion after starting my M3 the 'abs' and 'brake' light will stay on until I roll the car forward a few feet. Never used to do that until a few months ago. Dirty abs sensors or worn electronics?
                        Jason

                        '88 Zinno M3
                        '78 IHC Scout II
                        '99 Ducati 996

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                        • #13
                          Originally posted by Sbailey294 View Post
                          I was told that the "rev car to start the alternator" was a common M3 quirk.

                          If I release my handbrake, my dash lights turn off and it starts the alt. just like when I blip the throttle. I have always wished for an easy fix to this.
                          I also have to give my M3 a gentle blip on start-up to get all the dash lights to go out. Always wondered about this.
                          Motorsport 16v

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                          • #14
                            Originally posted by Motorsport 16v View Post
                            I also have to give my M3 a gentle blip on start-up to get all the dash lights to go out. Always wondered about this.

                            Me too...on both of my M3's...

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                            • #15
                              I don't remember where, but I thought I read somewhere that the lights are supposed to stay on until the alternator kicks in, which doesn't happen until 1500rpm or something like that. I could be wrong about that though.

                              edit: Oh, I just saw the earlier thread which mentions rev to start the alternator.
                              Last edited by ///M3 Terr; 12-24-2007, 03:09 PM.
                              Terrance

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