Under each key is a mechanism with four gold plated key contact wires that act as switches to complete the circuit between the tone generators and the drawbars when the key is played.
Figure 1, at left, shows a diagram of the key contacts when the key is at rest, or not depressed. Four individual signals from the tone generators enter from the right side of the diagram (through the green dots). These four signals flow through the gold plated wire key contacts. These key contacts pass through a mechanical "contact ram" (the vertical black line in the cener of the illustration). Note that the left side of each of the four key contacts is resting against the gray contact, which is connected to ground, essentially shorting out the signal from the tone generator. In this position, the key is turned off.
Figure 2 shows the result of depressing the key. The "contact ram" has been pushed downward by the depressed key. The four key contacts have now dropped away from the grounded position and now complete the circuit to the four red contacts. This action has the connected the output of the tone generators to the 16', 8', 4' and IV rank signals to the drawbar circuitry described in the next web page. The key is "on" in this position.
As you see, there are four individual key contact wires under each key on the single Continental Organ. As each single Continental Organ has 49 keys, that means that a total of 196 key contacts must be in correct operating order to allow the proper operation of the organ.