If the LED board is replacing the power led, remove the original power LED on the GBC by heating the two through hole legs at the back of the board
Add tape where the original LED was to avoid shorts.
The link cable pins and pin 1 and 32 of the cart may need to be trimmed to allow the board to sit flat. This will not effect gameplay at all.
Add solder to the pads. Make sure the are lined up with the pins on the board
If you are using screen kit which requires connection to the buttons, alternate pinouts can be seen below
