Re: [AMC-List] Blue light special HELP

[Tom Jennings <tomj@xxxxxxx>]

(oops, this ended up kinda long :-)


On Fri, 8 Dec 2006, Mark Price wrote:

> I know LEDS won't dim, I don't care I run dash lights at full.
> if I choose Leds, 
> which ones?
> Where do I buy them?
> 
> This may seem trivial, but it won't be easy for me to accomplish bulb changes after the final install, so I'd like to get this right!

Hell, you stare at the things the whole time you're in the seat,
you might as well get them right! I don't think it's trivial.


You CAN dim LEDs, they just don't dim as evenly with the dimmer
as lamps do; no harm done. I bought LED lamp replacements
from Digikey.  Digikey sells the latest semiconductor stuff to
industry and their interface is harsh and brutal and thorough
and good.

Go to their home page, www.digikey.com.

enter "LED lamp replacements" in the search box. Click search.

Next page, click the ITEMS IN STOCK box. Click search again.

You should get a table of items. AMC dash lamps are Wedge
base. There's a filter selection for "CAN REPLACE LAMPS..." with
194's. (The "red" vs "red clear" etc is just the color
of the enclosing plastic; it doesn't matter in dashboard
application.) You can CONTROL-CLICK or SHIFT-CLICK to select
more than one thing in the filter.

(To see the most lamps that might fit, I selected WEDGE and 12V,
ignoring the "CAN REPLACE..." column.)


I put some of these in my dash indicators (ALT, OIL, turns,
etc). For that they are a drop-in except as noted below...


Some warnings with LEDs in cars:

One, the light pattern. Incandescent lamps dump light in a
spherical pattern; there's just a hot wire throwing off light in
all directions.  LEDs are very directional; they squirt light
straight out. This is perfect for dash turn signal indicators
etc but lousy for dash gauge illumination. In an unrelated project,
I sanded the molded clear plastic "bulb" with 180 grit to make
a diffuse pattern. It helped.

Two, LEDs are a LOT LESS BRIGHT overall than incandescents.
The light produced within the narrow beam pattern is fine
(why they work so well for turn indicators) but if you spread
it out, it's pretty dim. There are multi-LED lamps for things
like taillights though.

(I'm working on illuminating the Hornet gauges with white LEDs,
but I bought a dozen submini LEDs and will carve a diffusor out
of PTEG plastic and fit it around the gauge faces. I already
did this to the heater control, it worked great.)

Three, they don't draw much current, which is 99% of the time
just wonderful.  But I have two problem areas, both fixable:

    * For the ALTernator light, it doesn't draw enough
      current for the alternator to start producing
      output! You'll have to rev the engine to about 2000 rpm,
      once, then the alt light will go out. I've been driving
      this way for a year. Next time I take the dash out I'll
      solder a resistor onto the back of the dash circuit board.

    * For the OIL idiot light, the oil pressure sender you;ll
      be surprised to see isn't exactly a perfect ON/OFF
      switch. When it's off (eg. oil pressure, dash light off)
      it may leak a few milliamps of current -- enough to light
      the LED! More scary, you wash off the engine, and a bit
      of moisture makes it pass 5 - 10 milliamps and the LED
      comes on bright! It's otherwise harmless, and would
      be fixed by paralleling a resistor onto the board.

      (The added resistor will consume current like the original
      lamp did; a #194 lamp draws .27amps, which you could
      simulate with a 68 ohm, 5-watt resistor. That's making 3
      watts of heat, which seems silly. I think something like
      .05 amps would do it (make the alt start; oil light out)
      which would be about 270 ohms, 1 watt. Probably less will
      work; I'll experiment some time.)

Four, some few of these LED lamp replacements are polarized. I
think just the bayonet-base ones, with the center wire is +12V,
and the brass shell is ground. Since I've never seen a car that
uses these lamps wired any other way it doesn't matter unless
you use an insulated socket with pigtail leads.

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