Let me take this for a ride. As equipped, your M880 came from the factory without a blackout light system. DOD saw the need to retrofit some of them and TACOM came up with a kit. The kit consisted of that 3 lever light switch you have, a harness, 1 blackout drive light that should be somewhere in the grill and 4 little rectangular lights, 2 at the front and 2 at the rear. The kit instructions show to cut the oval hole on the right upper dash in that little area that is angled towards the driver. The kit was obviously installed but 2 things may have occurred. Either the dash was replaced or the FD that had it, put a panel in its place with their own switches for the FD nighmare harness. The pic shows your switch in the serivce drive mode. This mode is necessary for normal operation. Voluteer firefighters not trained in 3 lever operations often fooled with the switch and presto, no lights. A trip to the mechanic parts changer netted correcting the switch. Many FDs found the need to remove the levers as your are, to avoid this. In your case they cemented their position bu dropping the switch behind the dash.
Now, blackouts are actually not blackout but a low level light so that vehicle operations can be carried out with less of a chance of aerial detection. The BO Drive light lets out a miniscule amount of light.
F Y I, the 266-10 isn't readily available in PDF unless you buy it on disc, a good investment I might add!