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Thread: Gen II - MIL "glows"

  1. #1
    Senior Member Fixit's Avatar
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    Gen II - MIL "glows"

    Info:
    - Key on... MIL flashes full bright for just a milli-second, then goes dim.
    - Not using the Ford supplied MIL lamp
    - I'm using a generic yellow LED in a custom housing I fabricated.

    When the engine is running, the MIL is not/ever totally "out". It glows at about (guessing) 10% brightness.

    Questions:
    - Is the Ford MIL an incandescent lamp, or an LED?

    Ideas:
    - If the Ford lamp is a traditional incandescent, thinking to install a "pull-down resistor" (of the same value as the Ford bulb) across my LED... (not to be confused with the current limiting resistor already in series with the LED.)

    ??
    John D. - Minneapolis 'Burbs

    1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
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  2. #2
    edwardb's Avatar
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    99% sure the Ford supplied MIL is an LED. On my Gen 2 #8674 build, I also switched to an aftermarket dash mounted LED. It too just barely glows all the time. Can just see it in the daytime. A little more visible at night, but not obtrusive. I've never had an actual "MIL ON" event (knock on wood) but I introduced some faults during testing and it definitely glows bright and would be hard to miss. So I'm convinced it works OK, and have left it that way. I've heard from others their Gen 2 also glows slightly.
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  3. #3
    Senior Member Fixit's Avatar
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    One of the threads I searched came up with your very similar description of the MIL on #8674...

    I wouldn't mind the "glow" so much, other than I scrounged some really cool vintage bezels from a salvage/surplus outfit.
    They've got glass magnifier "jewels" in them. When a lamp is off, they're totally dark, when the LED is on, they are "IN YOUR FACE" bright... which is what I wanted from the MIL and turn indicator. The turn indicator isn't a problem, as it's off-axis with line of sight - and will grab your attention. The MIL is dead-on-axis and when on it's like an interrogation lamp in your face.

    TestPanel`01.png

    The "glow" isn't really bothersome with the MIL, but I'd like to have it off with no problems present.
    John D. - Minneapolis 'Burbs

    1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
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  4. #4
    edwardb's Avatar
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    It is possible to tone down LED's with resistors in-line with the +12v wire. There are ways to calculate the value needed, but you also need to know technical aspects of the LED like forward voltage. Or you can experiment and find something that works. I toned down the fan on indicator in my Coupe build with a couple 470 Ohm Resistors, 1/2 W, 5%. Subtle but helped. A similar approach may/may not help with the slight glow of the MIL. Not necessarily that resistor value either. Google "how to dim led with resistor" and you'll find lots of things to read.
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  5. #5
    Senior Member FF33rod's Avatar
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    If you put a resistor in parallel with the LED, it may help but it will also affect the real "on" condition.
    I am not familiar with the standard Ford MIL circuit, what is driving it - the output of a control module? Have you measured the output voltage in this "no fault" condition that results in the dim LED? Does it drive the LED directly or is there a series resistor somewhere?

    Steve

  6. #6
    Senior Member Fixit's Avatar
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    I disassembled the Ford MIL, and it is an LED... a cheap little orange unit with a current-limiting resistor jammed in the housing. My guess is it's a low-output LED (lumens), and it just isn't noticeable (maybe) glowing behind the lens.

    It is possible to tone down LED's with resistors in-line with the +12v wire. There are ways to calculate the value needed, but you also need to know technical aspects of the LED like forward voltage.
    I'm using a high-output/bright LED for my indicator, and have calculated/installed the current limiting resistor using 13.7v for the baseline voltage. I could "up" that value and see what happens, but there's the fine-line between worky & no worky...

    I'm guessing that the 0v/ground/neg output of the Ford 'puter isn't a true on/off clean output to 0v/neg. It's sneaking a reference to neg somewhere that's enough to make the LED start to light. The scary part is fooling around with the "load" on an output like this can fry the transistor(s) that are going low to engage the circuit.

    (Maybe have the Ford 'puter drive a 12v micro-relay....? Then there's a true disconnect (air) between it and my LED... hmmm.)
    John D. - Minneapolis 'Burbs

    1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
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  7. #7
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    A little help? My engine and harness is a Gen 1. I do not recall a MIL lamp or harness in the kit. It is very possible I over looked it and will go back and do some digging. Anyone able to enlighten me on whether, it is provided and where it taps in?
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  8. #8
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    After checking the instructions a couple of times and finding no mention of the MIL light, I called Ford Perf. No MIL for Gen 1 engine and harness. I will be able to use the programmer, but will not have it hooked up full time and do not have plans for an Ngauge.
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  9. #9
    Senior Member Big Blocker's Avatar
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    Just to throw some shade on this subject, most of Ford's computer circuits are of the "saturated circuit" type, meaning that the circuit is powered thru all devices at all times and rely on a transistor to close the circuit to ground when needed. This translates to the MIL LED being powered all the time and is waiting for an "error event" to happen to close the circuit and ground the LED.

    That being said, all transistors and LED's leak voltage to a pre-designed amount. It's this "leakage" that allows the LED to glow dimly under certain conditions . . . more than likely it's the transistor in the computer.

    Adding a resistor to the LED in series will dim it [further] to a point of our perception of "Off". Getting this resistance correct is a trial-n-error process, depending on which computer you are working with.

    Doc
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  10. #10
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    Fixit, my apologies for using your post for my question.
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  11. #11
    Senior Member Fixit's Avatar
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    Quote Originally Posted by Railroad View Post
    Fixit, my apologies for using your post for my question.
    Not a problem, it wasn't a hijacking... just an expansion on the issue!
    John D. - Minneapolis 'Burbs

    1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
    2013 F-150 Platinum - Twin Turbo 3.5
    2018 Mk4 Roadster - #9365 Build Thread

  12. #12
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    With your permission,,,, I was informed by Ford Perf the Gen I does not have provisions for a MIL lamp. I guess an ngauge could be used to monitor an codes that pop up.
    20th Anniversary Mk IV, A50XS Coyote, TKO 600, Trunk Drop Box, Trunk Battery Box, Cubby Hole, Seat Heaters, Radiator hanger and shroud.

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