9v Switch Help

[Salix12]

I have a 9v train layout similar to this.  I have two trains, one train parked in the green box and one train in the purple box.  I am trying to run one train at a time by using the switch tracks to only allow the electrical current to go through the aligned track.  Any ideas on how to do this?  I have tried to take apart a switch, but couldn't quite figure it out.

[Stereo]

My understanding of the switches is that the outer 2 rails are always energized, but the 2 that cross in the switch get switched, so you just need to switch both switches at the same time, and have the power supply somewhere else in the loop.  I know that'll work for stopping a train on your purple track, less sure if it's symmetric to green as well. 

[Dav1d]

What Stereo says is correct, you have to switch both switches together. They both need to be in the same direction.

What I don't  understand is how you get that layout - when I try it I get a gap, but the track is slightly flexible so it can work. 

[Murdoch17]

Are those standard 9V LEGO switches? They don't look like it...

[lego3057]

In my old H0 layout, I remeber the switches could be modified by cutting some connection under the switch. That would allow for cutting the current on the closed path. So if both were closed the train would stop. Can one do it with LEGO 9V?

[Dav1d]

30 minutes ago, lego3057 said:

In my old H0 layout, I remember the switches could be modified by cutting some connection under the switch. That would allow for cutting the current on the closed path. So if both were closed the train would stop. Can one do it with LEGO 9V?

There is no need to do that. Switching the track also switches the current. This makes operation very simple - a train can be put in a siding or loop and isolated easily. 

With the old 12V track switching the track did not switch the current - therefore one or more 7860 remote controlled signals were required.

The new FX Bricks 9V switches only switch the track they do not switch the current.  

[lego3057]

1 hour ago, Dav1d said:

There is no need to do that. Switching the track also switches the current. This makes operation very simple - a train can be put in a siding or loop and isolated easily. 

With the old 12V track switching the track did not switch the current - therefore one or more 7860 remote controlled signals were required.

The new FX Bricks 9V switches only switch the track they do not switch the current.  

I learned something. Thanks

[zephyr1934]

On 4/28/2026 at 10:23 PM, Stereo said:

My understanding of the switches is that the outer 2 rails are always energized, but the 2 that cross in the switch get switched, so you just need to switch both switches at the same time, and have the power supply somewhere else in the loop.  I know that'll work for stopping a train on your purple track, less sure if it's symmetric to green as well. 

 

On 4/29/2026 at 3:06 AM, Dav1d said:

What Stereo says is correct, you have to switch both switches together. They both need to be in the same direction.

To be more specific, the outside rail of your big loop is continuously connected, and the inside rail of your big loop is continuously connected. In the single track section that means both rails are always connected. Let's assume you put your power connector here (otherwise it becomes more difficult to explain). The lego switches are single point, i.e., only one rail moves to determine which track is connected. The switch is wired so that power switches with the point. So if you approach the switch on the single track section, the left rail of the left branch is always powered, the right rail of the right branch is always powered. If the switch is aligned to the left, then the switch also makes an electrical connection for the right rail of the left branch to be powered. Meanwhile, the left rail of the right branch is cut off. Or simply, both rails on the left branch are connected, but only one of the rails on the right is connected. Switch the switch to the right branch and it swaps, both rails on the right are connected while only one on the left is connected.

But there are switches on both ends of your siding. If they are BOTH aligned to take the inside track, then one rail on the outside track will be cut off. If they are both aligned to take the track, one rail on the inside track is cut off. But if one switch is aligned for the inside and the other is aligned for the outside, then all tracks are powered because one switch is connecting the inside track the other is connecting the outside track. Hence Dav1d's comment that they need to be together, in the same direction.