This instructable shows how to use an LED to illuminate a GBC cartridge.
Step 1: Materials
You will need:
-special screwdriver or small pliers
NO SOLDERING REQUIRED FOR THIS INSTRUCTABLE
NOTE: This instructable is easier to complete on a later model GBC cart, due to there being empty space at the end of the cart.
Step 2: Open Cart
First you must open the cart. It uses a tamper-proof screw, which is very annoying. You can do this using a special screwdriver, or use a small pair of pliers like I did.
Step 3: Get an LED and mod it.
You need a small LED, one that will fit inside the cart. If it is too big, you will not be able to close the cart.
You will also probably need to sand the LED's leads, so that they can fit into one of the holes on the now-exposed circuit board.
Step 4: Find ground, +3v, and insert the LED
Around the edges of most carts, there is a row of 'holes' which are all ground. The trace they are on starts from the last pin(32), which is also labeled as GND. Now you just need your 3 volts. There are many other holes, many of which are 3volts. However, most will cause the game to crash or not boot. You simply need to test them all with your LED until you find one which doesn't crash the game.
Then, simply tape down the LED. No soldering needed!
Step 5: Close it up!
Now simply close up the cart. You can put the screw back in, but I put a standard philips screw in instead.
I have tested this on a Mario Golf and a Micro Machines 1 and 2 Twin Turbo cartridge. I cannot guarantee that this will work on other cartridges, or on your versions. I take no responsibility for any damage this causes to you, the console, the cart, or anything else.