Since LED's are polarity sensitive and GM's interior lighting is turned on when the door is opened grounding the switch.

 Would LED's work wiring them into the existing wiring? I want to get rid of the incandescent lights. Or do I need to run a seperate power wire to do this?

 Lastly, I would like to be able to have them on a 3 way switch so I can turn them on independently from the door switches. Is that doable or can I just twist the dimmer on the headlight switch as normal to turn them on.

Sarge

I think I remember a thread a while back about using leds in your interior.  If I get a chance ill try to dig it up.

Here is a thread where someone used LEDs

http://www.c3vr.com/forum/forum_posts.asp?TID=60285&KW=i nstrument+led

 

decrepid1338838.4174074074

Led's are polarity sensitive as you say, current flows
in one direction only. The good news is that if you get
the polarity wrong the Led will simply block the current
flow, and therefore not glow. You cannot damage a Led
by incorrect polarity. HOWEVER....

1) A Led has a maximum continuous current rating, and
will expire instantly if this is exceeded. So you must
use a resistor in series with each Led to restrict the
current flow so that it does not exceed the maximum
continuous rating. As you are feeding it from a 12Volt
source, you can calculate the approximate resistor size
required using good old Ohms Law. If the max current is
20mA (0.02 Amp) then the resistor size you will need
will be 12 divided by .02 which is 600 ohms, so either
a 560 or 620 ohm (standard size) would do the job in
this example. The resistor also needs to have sufficient
power rating, which = V x I so 12 times 0.02 =
0.24 Watts so you would use a 0.5 watt (half watt) or
1 watt rating to ensure you don't create excessive
heat in the resistor. NOTE: this example is using
20mA for calculations. You will need to redo calcs using
actual correct LED continuous current rating.

2) Now for the bad news... LED's give out way less
peripheral illumination than incandescent bulbs, and
I doubt you will like the result. I suggest you set up
a test LED and resistor on 12V battery first and try
it out before you get too excited !! LED's are great
indicators when looked at directly, but don't actually
shed much light.

Phew. Hope this hasn't put you to sleep !!

Kiwi Chris

Excellent explanation Chris!

Can I assume from your explanation that the LED replacement bulbs the Vette catalogs are selling for taillights already have the resistors incorporated into the bulb?  Or is this something one would have to add to the existing wiring in order to use them?

I like the look of them for rear lights and maybe even back up lights, but would probably not consider them for the interior, myself.

Just like Mark said,"Excellent explaination Chris!"

Now I've got so homework to do figuring out resistors now.

Thanks fella's!

Sarge  

Yes, the tail light LEDs already have the resistors.  Some LEDs can be purchased with the resistors in place, but many do not.

If you do a bit of rewiring, you can use one resistor in a harness feeding all of the dash lights.  But unless you put every bulb as an led, the other standard bulbs won't light with the resistor in place.  You might be able to use multiple LEDs in place of one bulb to shed some more light.

Bare LED's purchased from an electronics shop will not
usually have resistors built in - as the manufacturer
cannot know the circuit voltage the user will be working
with it cannot be determined in advance. However LED
products manufactured for specific applications (like for a car) can be produced knowing that 12V will be
used, and therefore can be manufactured complete with
resistors or other self current limiting / regulating
included. The only sure way to know is to ask prior to
purchase, or check the specs for the product.

Another bit of useful knowledge when working with LED's
is that their "apparent brightness" can be greatly
increased by feeding them with a "pulsed" supply. So
instead of a straight 12V DC, if they are fed with
12V which is being switched on and off at say 100
times per second (easy to do with electronics) and the
off and on times are the same duration (which equals
what is called a 50% duty ratio) then the LED can be
operated at twice the apparent current rating because
it is only on for half the time therefore equating
to the same average continuous current. Aha ! But
why would you do this ? Because one of the properties
of LED's is that they glow much brighter during the
power on transition than when just left on. Amazingly
some 5 to 10 times brighter for the same power
consumption. And if you change your duty ratio so that
on is 20% and off is 80% then you can crank the on
current up even further. That is when the "peak
current" value for a LED comes into play, which should
not be exceeded during each pulse.

So if you were going to get serious about using LED's
you would install a wee pulsed power supply to feed
them, and use relays or transistors to switch this
through to the LED's as commanded by the original
wiring. Are you asleep yet ????????? !!!

I think the fancy new LED stop lights and indicators
you see on trucks these days operate exactly this
way, but the whole pulsing thing is all inbuilt
electronically into the unit so you just chuck normal
12V DC at it and the rest is just real bright LED's by
unknown magic.

Cheers
Kiwi Chris

[QUOTE=CeeDee]So
instead of a straight 12V DC, if they are fed with
12V which is being switched on and off at say 100
times per second (easy to do with electronics)
[/QUOTE]

Is the switching easy enough to build yourself, do you have a description/diagram?

You will need a little electronics knowledge, or a mate
with some electonics knowledge. The easiest way is to use a 555 timer IC (integrated circuit) which are a
couple of dollars or so. These have 8 pins, to which
you connect power, ground and a couple of resitors and
capacitors.

The choice of resitors and capacitors determines the
frequency and duty ratio of the output. A spec sheet for
the 555 containing all the necessary info is readily
available - I did a google search on "555 timer" and came up with a great link straight away...

http://www.uoguelph.ca/~antoon/gadgets/555/555.html

So then you just set up the output to be the frequeny
and duty ratio you want (a 50% duty ration will give
you a "square wave" outout) and connect this output
to an NPN power transistor (nutha dollar). The power
transistor acts like a relay but is solid state. feed
the 555 signal into the Base, connect +12 to the
Collector, and the transistor will provide switched
+12 at it's Emitter pin exactly as per the 555 signal
being fed into it, but capable of supplying much more
current. So this becomes your "switched" 12V supply
which you then feed to the resistor + LED pairs (via
relays/switches or whatever it is that will be
controlling them.)

This will be relatively easy stuff for anyone with a
bit of electronics knowledge/experience.

With the resistor/capacitor decisions, if you use a
variable resitor (also called a potentiometer) in
place of fixed value resistors, then you can play with
the frequency & duty ratio "live" by adjusting these,
and see the effect it has on visible LED brightness.
It's the sort of thing you would set up on your kitchen
table first and play with until you got it where you
wanted it.

So go for it and play ! Don't forget to let us all
know how you get on :-)

Well I lucked out. These LED "5 bulb" bars have an integrated resistor in them.

I purchased them from a vendor in Old Town, Florida last week. BTW, great cruise night there on friday.

They were originally meant for motorcycle application but they said they can be used in automotive application too. So I'll be busy installing them this weekend.