Light switch tripping
Here's the problem.  The cable between light 2 and S2 is what's called a switch loop.  Switch loops don't have neutral.  They have always-hot and switched-hot. These are the two wires you connect to a switch. 

If you want to wire by colors, switched hot is usually red.  You're seeing white because the store doesn't sell Romex in black-red.  The installer was forced to use stock black-white.  There's an exception to the rule allowing white wires to be used for hots in this case (however, it also says you must remark the wires by wrapping them with electrical tape or other method). So get some red electrical tape and mark both ends of the white wire as red. 

You never attach neutral to a plain switch, this would result in a short when the switch is turned on.  

The white wire in a switch loop is not neutral.

Switches get always-hot and switched-hot... and not neutral. 

Lamps get switched-hot and neutral. They can't use always-hot because then you wouldn't be able to switch it.    You would never splice switched-hot and neutral together, as it would be a short when the switch is turned on. 

This drawing shows the problem.  Joining switched-hot to neutral up in the light box is causing the short when the light is turned on. 



How do you tell if a white wire is in-use as a switched-hot? By following the wires and seeing if it


has black/colored tape (now required) 
is one of only 2 conductors in a switch loop (therefore it must) 
is landed on a non-smartswitch
is  spliced into a group of hots
goes directly to a lamp but there's another wire known to be neutral
lights up a voltage detector when the switch is on.  This can be a problem if the switch is broken.   To make this last one easier, best practice is to use the white as the always-hot, and the black for the switched-hot.