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How do I fit basic light signals to a layout?

If you have never had the pleasure or are new to wiring anything other than a controller to a layout then you are in look because installing basic 2 aspect light signals is one of the easiest things that you are ever likely to install.
What will I need?
  • A two aspect signal
  • An ON/ON switch (officially known as an SPDT switch) This kind of switch is required because you never want to switch the lights off, just flick between red and green.
  • Enough wire to go from your power supply (usually a controller) to where the signal is to be placed, then times the distance by 3
What power supply will I need?
A lot of older controllers have a 12V auxiliary port on the back, this will do just fine as although LED signals only require 3v, they will have a resistor built in to drop the voltage. Care must be taken though as some more modern controllers have a 16v AC auxiliary port instead. These are for operating point motors and will damage your signal so take a good look at the signage back of the controller before wiring.
If you haven't got a 12v DC auxiliary port talk to your local model shop for a suitable alternative.
Let's get started
1. Run a wire from the DC auxiliary terminal marked with a + on your power supply to your SPDT switch.
2. The SPDT switch will have 3 terminals on the back of it. Connect the power feed to the middle terminal.
3. From the other two terminals on the switch run separate wires to the signal.
4. The signal will have 3 wires coming out of it. These will consist of two plain wires and a third with a resister attached. Connect the wires from the switch to the plain wires on the signal (these will often have the same colour flex as the lights they are powering, for example, red and green).
5. Now run a wire from the signal straight back to the power supply. This will attach to the wire with the resister on the signal and the terminal marked with a - on the power supply.
And there you have it, a very simple circuit ready to go! 
As always, it is advisable to read the instructions for your specific signal as this guide is purely to give you an idea but you should find them to be very similar.
Posted in: Model Railway

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