The starting gate switch I usually recommend is a pressure triggered micro switch from Radio Shack. That way you can look at your starting gate then go to your local Radio Shack and look over the micro switches to decide which one fits best. Most are both NC and NO types (Normally Open vs Normally Closed) and either can be used as long as you set the timer the same using the timer setup utility.
A starting gate switch is not included with the kit because of the variation in the way stating gates are designed from track to track.
Pictured below is an example of the start switch installed on a Best Track aluminum track starting gate. It may be hard to see, but when the gate is closed the hinged metal bar that the car-stopping rods/bolts are attached to will press the switch lever keeping the switch closed as long as the gate is closed. When the gate release lever is pulled, the spring will open the gate and the switch will be released, triggering the start of the race.
Important note: Unlike the example shown here, you should always insulate the connections to the switch, especially on an metal track. This one is shown uninsulated just so you can see the wires connecting to the switch. I also recommend attaching the switch with screws or bolts, rather than the double-stick tape used in this example, although double stick tape can be useful for experimenting with switch placement to determine optimal positioning, or for a temporary installation.
