Step 1: Materials
-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
Step 3: Get an LED and mod it.
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
Then, simply tape down the LED. No soldering needed!
Step 5: Close it up!
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.