Here is an updated pin out to the MBC3 chip found in many Gameboy / gameboy colour carts.
Everywhere i looked i read it could connect to a 16mbit ROM chip.... BUT there was NO RA20 Pin marked anywhere on the diagram... Now there is. After much searching i think there is ONLY 1 game that runs a MBC3 and 16mbit rom chip.
This will enable you to connect a 16mbit chip to any MBC3 cart.[/url