OK, I actually mentioned they weren't connected several posts up.

I assumed you thought they didn't work because you couldn't hear the mechanism clicking as you depressed the thumb levers or pushed the brake handles inward.

Just to be absolutely clear, this is what I mean: Even though the thumb levers may spring back up when pressed, and even though the brake levers may spring back outward when pushed inward, they may need the cable to return the ratcheting mechanism inside the shifter. Or, how do you know it has all the return spring it needs, if the cable's not conected?

Your friend may simply have upgraded one of his newer bikes, leaving him with an extra set of brifters, and that's why they're on an old bike which isn't set up to use them.