Here I have drawn up a simple diagram to show how we wired the lights in the Diesel Depot.
We decided to install six lights and the bulbs in the lamps that we have used here operate at 6V. So, to allow their use with our 12V supply (an old Hornby analogue controller), we wired two lamps in series, thereby halving the voltage at each lamp.
These pairs of lamps were then wired across the supply in parallel, thus maintaining 6V across each pair of lamps.
If you prefer to wire the lamps in series, or if we had an odd lamp to install, then it is necessary to wire a suitable resistor in series with the lamp, which performs the same job of halving the voltage.
Because these lights are on the same supply as all of our coloured light signals, we also wired in a single pole, single throw (SPST) switch which means that we can turn them off and still allow us to use the signals.
To connect all of the wires we used terminal blocks but I think we might remove these and simply solder the wires as this clearly gives a more positive and reliable connection, provided you have a good, clean joint of course, and it also looks much neater too.
The Coal Depot has had the same type of lamps installed but, here, we have only used two so the wiring was a little simpler.
Finally, to help prolong the life of the bulbs, it is possible to use the Hornby Controller to slightly reduce the voltage and, hence, the brightness of the lamps. Of course, as we have used just the one controller, so far, this will reduce the brightness of all of the lights, including the signals. However, when the rest of the room is dimly lit the lights are still plenty bright enough.