Yes, you can send a trigger through the Accessory Connector. The first step is to set the Accessory Connector mode using the ‘a1’ command. You can then follow that with the ‘ah’ command to set the state of the output lines.
Sometimes, when trying to program and I run into a difficulty, it is difficult to determine whether the problem is a bug in my code, e.g. the serial port wasn’t opened correctly, or whether I am sending the commands incorrectly. That’s why I use a program called RealTerm. See this page describing how to send commands to StimTracker. Even though the commands are different, the instructions for setting up the serial port and sending commands are still the same. You can experiment with the ‘a1’ and ‘ah’ commands using RealTerm, and once you are comfortable that you are using these commands correctly, you can then implement them in Python.