Two switches between the joystick ports on my 7800

[JonnyBritish]

What are they for? They are not labelled and the instruction book does not mention them?

[NightSprinter]

Difficulty switches. Some 7800 games use them (like in Xevious to make bomb-dropping work off the controller's second button), and 2600 compatibility.

[Rex Dart]

Left is B (Basic), Right is A (Advanced). Games don't necessarily hold to those conventions though.

[NightSprinter]

Very true, Rex. Games like "Starmaster" for the 2600 can also use them to toggle the Galactic Map.