What does this switch (next to the Fire Arm button) do?

[skypickle]

In the pictures in the manual, it is in the down (OFF) position.

[kotor633]

Well on page 309 of the manual this switch is called the MINELAYING SYSTEM MASTER switch. Since laying mines is not implemented in the Mi-8 in DCS World (see page 305: "The armament systems of the Mi-8MTV2 helicopter include unguided rockets, cannon and machine guns, free-falling bombs, and airborne minelaying systems (not implemented in simulation)" this switch can be ignored.