Remove switch from three-way series circuit
How to bypass a plain (1-way) switch

Make sure the switch works now, if not you will lose your mind trying to make it work.   Turn the power off first at breaker or fuse.  Unscrew covers and pull switch out of box.  Photograph everything. Then 


Note any ground wires which go to the switch. Grounds are bare, green, or yellow+green stripe. 
Ignoring any ground wires, there are now exactly two wires going to the switch.  If there are not, STOP: you will not be bypassing this switch today, and post the photos on SE for advice. 
A wire you can't identify is not a ground wire! 
Remove the switch and splice together those exactly two wires.  
Remove any ground wires still on the switch.  
Do Not Touch any other wires which may be in the box.  


Push it all back into the box and fit a blank cover.