For ease of assembly, you should print some of these schematics and diagrams before you begin. In most cases you will want to view the images in 'full scale'.

Main Schematic
Breadboard Component Layout
Breadboard Wire Assignments
Resistor Assignments
DB-9 Wiring Layout

The USB breadboard should already be soldered to the main component breadboard as explained earlier. Mount the audio jack (start gate) to the interface box case. Also mount the gate status LED to the case. Using the Breadboard Layout, identify where the twelve resistors will be mounted. Be sure to follow the diagram and watch carefully how the holes line up. They must match these holes in order to be in proper alignment with the copper bonding tabs underneath. Solder in all resistors first (photo doesn't show RA3 resistor). Now all the wires can be connected and soldered into place using these Schematic photos Photo 1 , Photo 2 and Photo 3 as an aid including those from the DB-9 connector (this photo shows the wire color code). Note: observe the correct DB-9 gender connector and run the wires through the slotted connector holes in the case before attaching to the DB-9 connectors. To keep in unison with these diagrams, keep the widest part of the connector (pins 1-5) at the top. Carefully observe all wire color coding from the DB9-1 and DB9-2 connectors and that you have established their correct placements. Note: The color coding in this photo has no relevance to the actual wiring diagram color codes.

The wires going to any buss bar can be connected at any location within the buss bar. Also add 6 Header Pins as shown in the photo. These are known as the 'Kill Switch' which will physically disable lanes not required. The microcontroller is set up for 4 lanes, therefore if you have less than that, you need to place a jumper pin across the lane(s) not used. This keeps your system versatile for possible different tracks in the future. Therefore - if you are using all 4 lanes, NO physical jumpers are used (only the ability to do so).
Note: If you have 4 lanes and you are confident that you will always use 4 lanes, you can omit this step altogether. If you have 3 lanes and never in the future wanting to use 4 lanes and are confident enough, you can also eliminate this step and simply tie RB3 (from the microcontroller chip) to the positive buss bar. This will Kill lane 4 permanently. By using the same method, if you only have 2 lanes, you can tie RB3 and RB2 to the positive buss bar killing lanes 4 and 3 permanently.

A little extra time here can save you hours later if wired incorrectly. Check and double check your work!

When you are convinced that everything is correctly soldered, mount the breadboard to the standoffs and mount the DB9-1 and DB9-2 connectors. Be careful not to put strain on the connector pins or the breadboard wires, but mold the excess wires in a circular fashion. Note that some photos may not totally match the diagrams. Always use the diagrams versus photos for referencing.