This cartridge was used by Service Centers to test the functionality of Nintendo 64 Systems. A five page instruction pamphlet was included to ensure the Service Center employees would be able to properly run the various tests and also to be able to correctly identify the problem(s) with the unit. If the small red led in the top right corner came on during any part of the test, it meant the unit was malfunctioning in some way.
What many people do not realize is that the connector on top is for a j-Tag, which means this cartridge is able to be reprogrammed. This was done so that if any problematic bugs or incompatibilities between the cartridge and the N64 systems were found, the programmed information on the cartridge could be erased and rewritten with an updated revision. They were actually one of the more expensive pieces of test equipment because of this, and Nintendo kept the price high (close to around $500) to discourage the centers from possibly trying to sell these.