I'm glad i can contribute a little bit to the community. I play around with electronics at work with both high and low voltage circuits in addition to micro controllers.
Long roof , beermonkey and Fe3x, you guys make valid points. LED's typically have a very narrow angle that they emit light compared to a inconsistent bulb that scatters light in all directions. Due to the small angle LED's tend to have "hot spots" or have a pin point light source. I've tried with various gauge clusters on imports and domestics, there are a few ways to get around this, first is to add more LED's so that the light angles kinda mix together when using an array of them. Another is to sand down or scuff the top of the LED, max lumen output will be decreased a little bit however the way the light disperses is better. The simplest one is to just select a family of LED's that naturally have a wide angle. Some of the reasons mentioned is why those "bulb type" LED replacements don't work out too well. As far as the color goes, what others have mentioned will work very well, red LEDS for the red lights /lenses and "white" for the reverse lights and yellow /orange for the blinkers / side markers. LED's have a narrow wavelength emission , meaning that the "white" LED may actually be centered to a blue(cooler) or red (warmer) shift. This should not be a problem what so ever for just using them strictly as a lamp.
overall the benefits to the LED's are :
low power consumption ( not not need as much current / voltage to drive them)
typically operate cooler within conservative operation parameters than conventional bulbs
Overall lifetime is much longer than incandescent or fluorescent bulbs
The "turn-on" time is much faster, making it ideal for brake lights. Normal bulbs have a inherent "lag" as the filament heats up
Downfalls
Additional circuitry is required, resistors, ballast resistors, more LED's ect.
Pre-made units are expensive, better off making your own and learning something really interesting
Extreme cold climates, the turn on /off time gets affected and they operate "slower"
Some considerations when selecting components for this project:
select a wider angle LED, somewhere between 30 to 45 degrees should work well
consider the wattage specs for the resistors and LED's so they will not generate too much wasted energy via heat (IE 12V system @ 0.25W is about 0.02A )
here is a link for some decent 12V LED's
http://www.bivar.com/portals/0/products/5HX12V-X.pdf
Another work around is to use a lower voltage LED and step down the 12V to whatever is the spec you need. typically the higher voltage LED's will cost more
Use a drafting program like LtSpice that is free and use it to lay out the schematic for the proto boards
Consider the way the circuits are connected, a string of LED's connected in series and multiple strings connected in parallel, or all LED's connected in parallel
22 gauge should be good to use for wire leads, i use 22 gauge on 600V systems , however they are sub Mili amp currents.
Use Rosin core solder, I've seen plenty of guys grab that roll of solder they have had on the shelf for years, its a good bet that it may be acid flux solder (will corrode)
As mentioned before when finally assembled use some type of insulating epoxy. I like the Devcon stuff I mentioned about, it does not get rock hard and is easy to mechanically remove if re-work needs to be done and still does a good job of insulating / corrosion protection.
Sorry for the novel guys
