Aztec Adventure is basically Sega's version of the original The Legend of Zelda except that in this game you can bribe enemies to come along with you.
Sound Test#
At the screen before the start of the game, press Left once and Right 20 times. Select "00" to exit.
Level Select#
At the title screen, press Up 5 times before the scroll opens, then press Right 3 times when Nino (red hatted character) tosses money at everyone else, then press Left as the characters walk off the screen. The level number will appear next to the title. Toggle it with Up and Down and start the game to go to the chosen level.
(Source: GameFAQs (Vegetaman))