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LED PCM monitored status lights?

Discussion in 'Performance Lighting' started by 2000StreetRod, February 13, 2014.

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  1. 2000StreetRod

    2000StreetRod Staff Member Moderator Elite Explorer

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    I decided to replace my instrument cluster illumination lamps with LEDs while I had the cluster out to fix my 5 x 5 chimes alert that the air bag lamp is nonfunctional. LEDs last longer and draw less current. I'm also considering replacing some of my status lamps with LEDs since its a pain to remove and install the instrument cluster. I know that the PCM monitors the air bag lamp since it detected it had failed (wasn't even installed). Since LEDs draw less current I'm concerned that if I replace status lamps monitored by the PCM it may detect them as failed. Does anyone know which status lamps can be replaced with LEDs without causing a detected failure?
     
    Last edited: February 13, 2014
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  3. MustangP51

    MustangP51 Well-Known Member

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    If you replace the indicator bulbs with LEDs the PCM will detect them as failed. I would think that if you added a load resistor to the circuit you could dupe the PCM into thinking there is a bulb there. Have not tried it myself so ill only say there is a possibility of it working.
     
  4. 2000StreetRod

    2000StreetRod Staff Member Moderator Elite Explorer

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    infrequently illuminated

    So far I've not found any bulbs that are burned out - not even the backlights although they're pretty darkly glazed over and of various resistance values. Since the indicators are only on briefly unless a problem is ignored and not corrected, I can't see any advantage to LED replacement for any bulbs except the backlight ones. It appears the THEFT light is already an LED since it glowed red when I was checking resistance with my meter.
     
  5. DjDom

    DjDom Moderator Emeritus

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    It should be fine if you put a resistor inline with the bulb.
    Most 194 LEDs have enough room in the plastic housing that plugs into the socket to fit a resistor.
     
  6. 2000StreetRod

    2000StreetRod Staff Member Moderator Elite Explorer

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    LEDs & 74s

    I've finished testing and replacing (as desired or needed) all of the lamps in the instrument cluster. Not even one bulb was burned out and the only bulb/socket missing was the airbag lamp. Even the bulb for the 4x4 high, 4x4low and air suspension were functional although I don't have any of the capabilities. I found one bulb position marked HAZ and traced the wiring to find it marked as unused in the wiring diagram. I replaced all 6 illumination lamps with 194 style 5 SMD LEDs. I replaced the ten most often used indicators (Check engine, cruise, turn signals, O/D off, airbag, etc.) with new type 74 incandescent bulbs.
    LED&Lamp.jpg
    I made sure every lamp illuminated before and after being installed.
    Cluster1.jpg
    I have four LEDs left over so I'll probably replace the illumination lamp in the HVAC control panel with one.
     
  7. DjDom

    DjDom Moderator Emeritus

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    I love you for this picture man.. I'm going to replace mine with LEDs very soon and didn't know which way positive and negative is.
     
  8. 2000StreetRod

    2000StreetRod Staff Member Moderator Elite Explorer

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    no polarity markings

    There are no polarity markings on the LEDs that I purchased and I was unable to determine the polarity using an inexpensive ohmmeter. I used a 12 volt battery trickle charger and some small alligator test clips to determine the correct connection. Upon closer examination I've noticed that one lead on each of my remaining LEDs is larger than the other. I'll test them to see if that is a way to determine polarity. The instrument cluster flexible printed circuit board has polarity marked for the Theft LED only. It is a multi-layer circuit board and I would not have been able to test the installed LEDs without referring to the wiring diagram for connector pins. I removed the Theft LED during testing since it may be a lower voltage lamp. If it would be helpful I can post the connector and pin numbers to test the illumination lamps.

    Edit: On my LEDs the smaller diameter lead should be connected to the positive supply and the larger diameter lead should be connected to ground.
     
    Last edited: February 21, 2014
  9. 2000StreetRod

    2000StreetRod Staff Member Moderator Elite Explorer

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    LED testing - 2nd generation instrument cluster

    This post describes how to test the 2nd generation Explorer instrument cluster illumination lamps when replaced with LEDs. There are 6 lamps that are controlled by the dimmer switch. They are identified by the large black lamp sockets in the photo below.
    Cluster2.jpg
    LEDs are polarity sensitive and will only illuminate when the correct power polarity is observed. There were no polarity markings on the LEDs that I purchased. On my LEDs the smaller diameter lead should be connected to the positive supply and the larger diameter lead should be connected to ground. If one doesn't light when tested then disconnect the power source, remove the socket/LED lamp, rotate the socket 180 degrees and reinsert. The C numbers are etched into the flexible, multi-layer circuit board as are the first and last pin numbers for each connector.

    Etched . . . . wiring diagram
    number. . . . number
    C1 . . . . . . . . C286
    C2 . . . . . . . . C287
    C3 . . . . . . . . C288

    Note: pin numbers for C288 increase in the opposite direction to C286 & C287

    C1Pin8 +, C1Pin7 - illuminates A & B
    C2Pin4 +, C2Pin7 - illuminates C & D
    C2Pin4 +, C1Pin7 - illuminates E & F
     
  10. DjDom

    DjDom Moderator Emeritus

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    Very thorough explanation. I just need to wait until it's warmer out.
    You can check the LEDs with a 9V battery, should be enough to light them.
     

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