3-WAY-SWITCH  &  4-WAY-SWITCH
How-To-Do  vs.  How-To-Know

```This is a typical (right!) picture out of a "Do-It-Yourself" book:
3-WAY-SWITCH = "How to wire a lamp fixture with 2 independent switches"
It explains  "How-To-Do"   B U T   N O T   "How-To-Know" !

My 13 years of experience in USA neigborhoods as the
"Helping Hand of Our German Engineer" tought me,
that this task seems to be a "Master's Job":

If anything is different, or, something wrong wired has to be fixed:
There is a "Big Problem" - Because there is no knowledge behind!

(1st) You have to know how the SWITCH is wired inside
and (2nd) You have to know the WIRE-DIAGRAM ...

Observe the (!) "Wire-Crossing" - It has an advantage:
LAMP = OFF, when BOTH SWITCHES are DOWN ( or UP ),
LAMP = ON, when ONE SWITCH is UP.

When you have understood the diagram, than it is easy to extend.
If you would like to have a third switch to control the light:
Add a "4-WAY-SWITCH" in the DIAGRAM's (!) "Wire-Crossing" area ...

4-WAY-SWITCH  in DOWN-    &      in its  UP-Position

... LAMP = OFF, when ALL SWITCHES are DOWN

R E M A R K S :   The naming   "2-WAY",  "3-WAY",  "4-WAY"  is misleading:
+------------------------------------------------------------------------+
|  With  "2-WAY"-Wiring  you have  1 way   to switch the light  on/off;  |
|  with  "3-WAY"-Wiring  you have  2 ways  to switch the light  on/off;  |
|  with  "4-WAY"-Wiring  you have  3 ways  to switch the light  on/off.  |
|                                                                        |
|  OR:  " WITH 3-WAY-WIRING  YOU CAN MAKE AT LEAST  3  M I S T A K E S " |
+------------------------------------------------------------------------+
Much more appropriate would be  "2-WIRE"-,  "3-WIRE"-,  "4-WIRE"- SWITCHES

impressum:
**************************************************************************
© C.HAMANN        http://public.beuth-hochschule.de/~hamann       01/15/11

```