Beginner Analog Multiplexer Wiring Help
If you're using a CMOS analog multiplexer such as a 74HC4051, you must connect all digital inputs to the proper logic level (it's okay to let analog pins float). 

In your case, you seem to have left the ENABLE pin open. It needs to be tied to the appropriate level (low in the case of the 74HC4051 since it's actually an /ENABLE input). 

Edit: You have a 74HC4067 which is similar to the 4051 but is 16:1 rather than 8:1 (and which is why you have 4 address inputs, which again need to be tied to a specific logic level).