Regardless if you are building your own project or purchased it already built, you will still have to prepare the track that you will be using. There may be several different styles in track design, so you will have to improvise to what works best in your situation. I can only show you the way I did mine, but there can be several methods to achieve the same results.
    Install one or two furling strips of wood underneath and at 'right angles' to the track near where the sensor holes will be drilled to act as a spacer for the photocells. This will allow room for the sensors and a place for the wires to run and attach. Note: There are several methods that can be used to mount the photo transistors. It just depends on how much time and effort you want to apply. Just a simple hole can be drilled thru the track for the sensor and merely pushing the sensor in the hole (however not recommended). Another method see Photo. What ever works best for you. Drill a hole evenly spaced in the lane centers in a straight line (these need to have the same spacing as the Tower overhead LED's). The way I did mine was to drill 3/8" holes and I used the 3/8" lamp 'all thread' brass tubing by cutting the same depth of the track surface. Use a hammer and hit the all-thread pieces into place until flush with the track surface ( support the bottom side with a socket or something to prevent any splitting). Apply heat shrink to the leads of the photocells making sure to note which is the collector and emitter leads. Also mark which lanes numbers are which. One method is by using a cork (#0) as a holder to install the Photo transistor. This way the sensors can be easily removed. It should look something similar to this (showen without corks). When done, the photo transistors should be about 1/8" below the surface of the track. Any less and it might pick up false triggers and any more might cause improper responses to the exposed light source. You might want to use a temparily board that simulates your track to build your sensor harness as you see in my photos.
 nbsp;nbsp; Now is the time to wire the DB9-2 cable to the Photocells. You will be using 5 wires in the DB9-2 cable. Use this schematic (top righthand side) and this diagram and follow the same wiring scheme as before. Very important- pay close attention to which is the collector and emitters on the photo transistors. The short lead is the collector. Be careful when using heat shrink with the heat gun because the frail insulation on the cat5 wire melts easily. Tuck the wires along the furling strip carefully. Use a cable clamp to secure the cable to the track end (see in photo).