I have a client who has 3 sets of three way switches one set on each floor. The purpose so I am told is that who ever enters the hallway can either turn on the hallway lights (on all three floors) or shut them off at their respective door entry. The second of the set again I am told is to turn on or off the outdoor lights once again shared by all three floors. The problem from what I can see is that yes on one floor the hall lights go on and off and yes the outdoor lights as well work with the second side by side switch... here is the catch the other floors have to have the switches in certain position or non of them work. So there is only one point of the three floors with the service the way it was intended. If someone should come out of the third floor apartment and flip a switch not only would they not get light but now none of the three floors run anything! Any of this make sense to anyone... HELP

Home-Handy-Man- Services - Let me susjest this ,go to Lowe's and get you a book on ELECTRICAL, one that showes pictures of what you really need, I know they have some that is really good because my younger got one there, it only run him about $5 or ^ dollars, it showed how to do 2 way 3 way 4way switches from start to finish , hope this helps If it does ,rate my answer below Good luck & GOD BLESS:::: F.B.E.

You mentioned 3 sets of 3 way switches. If you are controlling one set of lights from 3 switches then you need two 3 way switches at the ends of the circuit and a 4 way switch in the middle.

Forgive repeating above. When switching from 2 locations, you use 2 three ways, to add a 3rd, 4th, or more switches you need to have a 4 way(s) in the middle.
3 way circuits have 2 wires(Travellers/usually same color) that go from bottom switch, to middle floor switch, then to top floor switch, The pair from the bottom needs to connect to 2 same colored screws on the 4 way(at middle floor), the 2 that go to upstairs connects to other 2 screws on same 4 way, The top and bottom 3ways need the 2 Travellers to connect to the 2 same colored screws on three ways. You now have 2 3 ways(top and bottom floor) that are lacking a wire on the single (common) screw. One end MUST have a constant Hot, the other(doesn't matter which)Must to go to the lights hot wire.
One end is called "The Hot End) the other (The switched end).
You will have to repeat for second set of lights. If it never worked, may not be enough wires, There are solutions with X10, which will work with your existing setup. I prefer no electronics, unless needed, however, X10 may be an easy way out, May or may not be more costly.
Good Luck