Original instructions by Michiel van Wessem with revisions and diagrams by Kent Williams.

The E30 on-board computer (OBC) has an orange-tinted LCD display that is illuminated from the back by little incandescent bulbs. When these little fireflies die, you're supposed to replace the light assembly. It's a nuisance because it's a pain to get to the light assembly, and it's also rather costly -- as much as $30 for the assembly. 

These instructions will show you how to substitute LED's for the standard 6-volt bulbs. LED's (light emitting diodes) are durable. Their exact life span is still unknown, but is thought to be at least 100 years. 

This solution works excellently.  At the top of this page, you can see a photo of the finished light assembly with LEDs.  Since Gustavo Melo has very thorough instructions for removing this light module in a separate forum article, that aspect of the project is not covered here.  This assumes that you have already removed the module from the OBC.

Note: this procedure is only suitable for people with good electronic soldering skills. Component leads are cut short and soldering will have to be done very fast to avoid overheating the components.  You'll definitely need a low wattage soldering pen.

Two LEDs and a resistor are put in series. The LEDs are super bright orange (620 nm) LEDs with a 45º viewing angle. I bought a pair from Mouser Electronics for 50 cents each (plus shipping).  You might want to order an extra one or two just in case you break off one of the leads.  Mouser stock # is 512-MV8742. The resistor is 390 Ohm, 1/2 Watt and five of them (that's the way they're packaged) at Radio Shack costs 79 cents. 

This is what the little PCB looks like after you unhook the white plastic piece and you de-solder the bulbs on the bottom of the board.   You can discard the incandescent bulbs and their little white holders;  you won't reuse these.  With a pen I marked where the positive and negative (ground) connections are on the board. Make sure to connect the LEDs with the right polarity -- they are diodes. You can kill them if you reverse them. The anode is the lead that is supposed to get the positive voltage. One way to recognize the anode is that the lead is a little longer. The name of the other lead is cathode. Another way to tell anode and cathode is to hold the LED with its legs down and you look at the insides;  the anode ducks under the cathode. (See the figure below for clarification)

Now, you stick the anode of one LED through the hole that is marked + on the PCB board and solder it on the other side. The cathode of that LED is trimmed short (about 3/8" to1/2" long). With the other LED, you stick the cathode through the hole that is marked -, solder it there and trim the anode short. Move the LEDs so that they stick up at about 15º. Now, take the resistor and fold the leads back in sort of a loop. Cut them about a quarter inch from each other, so they won't be able to touch. Now, solder the resistor between the short cathode from one LED that is sticking out and the anode of the other LED. You'll have to solder this one fast, or things will overheat and die.  You need to tuck the resistor in close to the anode and cathode legs that are soldered to the board.  The resistor will almost be touching these leads.  If you don't position the resistor in this way, you'll have a hard time fitting the plastic reflector/cover over the LED's.  It's kind of a tight fit.  See the diagram below for more detail.

Now you can clip the white plastic reflector plastic back on, stick the light assembly back in the OBC, turn the ignition key on and behold!  You should never have to change the backlight again. 

An additional benefit is that the LEDs use less power then the incandescent originals... about 225 mW for the LEDs versus about 680 mW for the fireflies. Because of this, you'll have less alternator drag so more fuel efficiency and more power! :)