I bought a large blue LED at Radio Shack, and mounted it an Estes Electron Beam launch controller. I wanted a launcher that would operate with low current igniters, and the current required to drive an incandescent lamp is way too high for many igniters. Since most LEDs have about a 20mA draw, this means it is safe for probably most igniters, especially the Quest igniters. This LED I chose is just an LED, and so a current limiting resistor was required. I soldered it to one of the LED leads, and it does not matter which -- but the LED polarity does! This particular LED is huge, and about the same size as the bulb that was in the Electron Beam. I epoxied it in, and then soldered the resistor lead and the LED lead to the brass strips inside the controller that contacted the bulb.
I'd recommend checking out ledcalc.com if you do not know how to calculate the LED current limiting resistor values. It is pretty neat, and shows the circuit, you type in the values of voltage and current from the LED's specs, and it calculates the resistor value, and actually displays a resistor with the correct color bands. Since resistors come in specific values, it will recommend the correct resistor to buy. For example, if the program calculates that you need 110 ohms, it will suggest 120, since that is a common value. It will pick a larger resistor value, to force a lower current (i.e. safer). I picked a smaller resistor for mine, driving it at about 23mA, which is fine for most LEDs. Bear in mind that they specify a current that is known to be safe, so a little more is usually not an issue.
. I've seen it done both ways (led resister wiring), they both have pros and cons, if neatness doesn't matter then attaching the resister directly works fine, otoh it is somewhat messy(even more mess if you need more than 2 resistors. doing a circut board makes a neater install and 'portable' if you need to transfer things, if you can't find a 'standard' board it will take longer.
