Lego track switch doesn't close properly
Warning: LEGO pieces were harmed for this answer

How the switch works


So, how does it work then? Well, let's open it up!


The back plate is held into place by 14 pins. We'll carefully pry it open with a knife. Alternatively, we could use a drill bit to slowly scrape off the pinheads. 

Both methods are destructive. The back plate needs to be glued back on later. 

Once we can lift off the backplate, we already got the slider. 

Next we'll unplug the switch. Let's take a pair of pliers and carefully -just a bit!- squeeze the peg, then push it out. 




Yellow: The slider is of a soft plastic. Notice the oval hole with a nose. When you move the slider this bit gets squeezed and then snaps into position. There's two stops, they have a figure 8 shape.
Red: At the end of the slider there's a single tooth. This tooth flicks
the switch.
Green: The switch has a peg and a spring. The spring has two legs. 
The tooth    is supposed to sit right between them.


What's next?

So much for starters. Now, what about your points?

In any case, use some compressed air first. Switch them repeatedly. Maybe it's just a grain of dust. Still not functioning properly? Can you still return them?

Okay. Let's triple troubleshoot:


Is the slider stuck?
Can it move freely? Does it 'snap in'?
Does the spring have enough tension?


If the slider's malfunctioning, you'd have to remove the back plate. However, if the spring's your suspect there's a less destructive way. 

How to access the peg only


In theory, one could try to pry out the switch with a flat
screwdriver. I didn't dare it. Parts could warp, the peg could break
and I think LEGO did their best to prevent creative kids from doing
it.


But take a look at the back plate. You can barely see it, but there's a circle. It's right on top of the peg.





I took a drill bit and started to slowly scratch off some of the plastic. Once the tip was through, I finished off the rest with a scalpel. 

Take your time! The plastic is quite thin and the peg's right under it. 

I could now easily access the peg with my pliers and push it out. I adjusted the spring and lined everything up. 

How to access the spring

This might also work, but I don't recommend it. I gave it a try. It's way too fiddly. 



Take a scalpel and cut a hole in the side of the switch. 
Now you can take a peek inside. See if the tooth is off-center. If so, try to lift the corresponding leg of the spring with a needle. Good luck.