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LED light bulb swap lessons learned

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  • c4clewis
    Experienced
    • Aug 18 2010
    • 117

    LED light bulb swap lessons learned

    Two things that came up as I have switched just about every bulb over to LED's in the Tbird.

    1) You need an ELECTRONIC NO-LOAD flasher. Once I installed the bulbs, there was not enough amp draw to make the old flasher flash. I went to the local parts store and they tried to sell me a "LED compatible flasher". It was the same flasher that I had installed. I got my no-load flasher from my local 4x4 store.

    2) This one drove me crazy. I swapped from a Powermaster alternator to a Ford 2G from a 1991 Taurus because I have learned that having replacement parts that you can get locally is way better than having to order and wait... especially when your alternator dies going into a car show.
    When I reworked my wiring, my GEN light stayed on. Hmm, so I checked the wiring. Nope, looks right.

    Researched any problems online... nope looks correct.

    Went through all the wiring with a multimeter... nope looks correct.

    The only thing that I didn't have was a resistor in-line with the dummy light to keep the alternator charging if the light burned out. Then I got to thinking... those LED's don't draw much in the way of wattage. I swapped out the LED for the original incandescent... works perfectly.

    I still don't know why it worked with the Powermaster 3 wire and then didn't like the Ford 2G series alternator, maybe someone here is smarter on why.
  • simplyconnected
    Administrator
    • May 26 2009
    • 8779

    #2
    Originally posted by c4clewis
    ...I still don't know why it worked with the Powermaster 3 wire and then didn't like the Ford 2G series alternator, maybe someone here is smarter on why.
    Because your PowerGen is a GM alt that normally uses FOUR wires. They have a GEN light wire and a 'sense' wire (that PowerGen wired internally).

    Ford alternators need a small key-switch current to activate the regulator. Ford integrates the 'sense' with the 'GEN' to make it work the way you would expect. The only problem (if it is one) with Ford alternators is, without that shunt resistor around the bulb, if the bulb breaks or burns out, the alternator won't know the key is on so it won't charge.

    There are other concerns with using an LED in the GEN light...

    LEDs are diodes that stop current flow in one direction and they are polarity-dependent.

    LEDs only pass .02-amps when on. The alt needs more than that to sense your key is on but the LED is limiting current at .02-amps. It's no wonder the LED is on all the time. Furthermore, the alternator might overcharge your battery because it doesn't see full battery voltage through the LED and it will overcharge the battery.

    So, re-engineering the charging system by replacing the incandescent GEN bulb with an LED simply won't work. If you don't like the GEN light, it may be replaced with a simple resistor. Personally I LOVE that GEN light, especially in my cars with one belt. I need to know if the water pump stops moving. - Dave
    Member, Sons of the American Revolution

    CLICK HERE to see my custom hydraulic roller 390 FE build.

    "We've got to pause and ask ourselves: How much clean air do we need?"
    --Lee Iacocca

    From: Royal Oak, Michigan

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    • c4clewis
      Experienced
      • Aug 18 2010
      • 117

      #3
      "The alt needs more than that to sense your key is on but the LED is limiting current at .02-amps"

      That's about what I figured. Just passing on the lesson learned.

      Comment

      • Djweaz
        Experienced
        • Apr 14 2016
        • 101

        #4
        I have LED headlights in mine. They require 12v to work. I had them in my 55 Sedan Delivery courier and it used to stump me sometimes the head lights wouldn’t work but driving it around the block they would come on. That’s when I figured out the voltage they needed. Works the same way as my 59s he4s. I added to the 4 taillights with LED lights. I was surprised that they worked turn signals and all. The problem that did happen was when turning them off, brake,turn signal, tail lights, they stayed on but really low. Not enough to see it in the daytime but when it was dark. So I put back in the normal tail lights. For my headlights I got tired of driving at nights with high beams on and still not being able to see. Then you have the jerks that will flash you because you have the hi beams on. Don’t have that issue now my head lights light the road up bright as day
        Rob
        1959 Thunderbird J-Code
        Tbird registry
        #15794

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