what does this &%$#$ switch do ?

Could be your automatic disconnecting differential switch... see if this has any info that helps.

Now i'm really confused because that article says that Toyota uses live hubs on the trucks with ADD but I have manual hubs.

Might take it by a Toyota dealership and ask them. I'm not personally familiar with 4wd vehicles, I just do a mean web-surf and have ready access to a Haynes manual on my vehicle. ;) Does your truck not have an owners manual in it? I assume you're not the original owner. Dee

ADD is automatic, only a switch inside the transfer case that engages when you shift into 4WD. Perhaps it is the "deck light" that turns on the light for the bed. If its like the one in my 4Runner, it only works if the parking lights are on as well.

allows you to crank the engine without the need to push the clutch in, gets you out of the hole when your engine won't start 'cause you went too deep into that "small puddle".