Below.  Drawing of bulb exchanger.  When one bulb burns out, a solenoid is activated allowing a new bulb to swing into position.

Above.  Sighting device used on high or mast mounted color light signals with modular light units.  The device is used to help properly position the signal given its relatively narrow light beam.  It is located in only one of the light units.  The background or target needs to contain a hole to accommodate the device as shown in the photo on the left.

Left.  Light units without the sighting device have a cover installed.