Quite a while back, Canon used the T3 proprietary connectors on its line of EOS film cameras. Now, the T3 it is obsolete; replaced by N3 and E3. The T3 connector is actually very similar to the N3 connector; it has three pin connectors that are configured in a happy face formation. But unlike the plug-in N3 connector, it is a screw-in type. One of the pins on the T3 connector is indented. All three pins are spring-loaded and can fully retract into the connector body.
Looking at the Canon T3 connector on the male side (on the remote switch), the following is its pin-out:
Left - Shutter
Right - Focus
Bottom - Ground
The way the pin-out works is very simple. The camera fires when the shutter pin is shorted to ground. When the focus pin is shorted to ground, the camera focuses.
The Canon T3 remote switch has a single two-position. In the first position, the focus and ground is shorted together. In the second position, all three pins are shorted together.
When you make your own remote switch, it is possible to separate the functionality into two different switches.
Unlike the E3 connector (see RS60-E3 articles on this site), which is a standard 2.5mm sub-mini connector used in the audio world, the T3 connector is proprietary made by Canon. Neither the male nor the female connector can be source from anywhere. The best bet is to buy an accessory or cable adapter with these heads and cut it off for your project.