I'm looking for a wiring diagram or some information about the internal connections of this switch from the blue train era.

LEGO 12V switch

It is used for controlling the automatic points, and is visible on the original box:

LEGO automatic points

The points connect to the back of the switch using a 3-pole connector:

LEGO 3-pole connector

I want to use a microcontroller to operate the points without manually pushing buttons. Since I don't have any of these, I cannot measure the connections (using a multimeter).

Does anyone own this switch, and cares to share some information?

This is how I think the switch works. I have tried wiring it this way and it works, however the points barely move. Perhaps the problem lies with the solenoids inside the points?

LEGO switch schematic

1 Answer 1


In electrical engineering one might call it: DPDT (Double Pole Double Throw) Momentary (On)-Off-(On) Reversing Polarity Toggle Switch.


Momentary in this configuration means that it's spring loaded towards its centre position.

Edit: I'm not sure though, see the comment below. I have the remotely controlled switch points from the gray era and they work like above.

  • Are you sure it is a momentary switch? The 2-pole power supply connects to the side of the switch, and a 3-pole connector connects to the back leading to the points. From what I can see in the pictures it looks like the switch is a normal toggle switch with only two positions. Though I can't be sure. The points itself have a built-in switch which is toggled once the points are in position, unpowering the solenoids.
    – Midas
    Commented Jan 23, 2017 at 13:34
  • You might be right.
    – Niels
    Commented Jan 23, 2017 at 13:56
  • Yes, it looks like there is a difference between grey/blue era. The blue ones use two solenoids (one for each direction), so I guess the grey ones use one solenoid only (reversing the polarity to change the direction).
    – Midas
    Commented Jan 23, 2017 at 14:17
  • I've updated my question. Could you take a look?
    – Midas
    Commented Jan 23, 2017 at 14:40
  • I might ask TLG for this. There are several possibilties. I didn't know the switch has a 3-pole output. If it moves barely the two solenoids might be in series, but then, mentioning the interlocked end switch might obstruct power flow to switch back again. I don't like re invent the wheel. Neither do I own the switch nor the railswitch so I can't find out. What we need is a datasheet. TLG can clear this up for us.
    – Niels
    Commented Jan 23, 2017 at 18:34

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