Oh crap! edgji, if you connected a wire from the Spark 3.3v to the terminal C of the zerocross tail you may have damaged the output transistor of the tail by passing 3.3v and no current limit through it.
You can test the output by connecting the cathode of an LED (the negative side, usually the shorter lead) to the C terminal and the anode to a 180 to 200 ohm resistor with the other end connected to the Spark 3.3v. If the LED lights that is a start. If it is “blinking” at 60Hz and appears somewhat dim, that is very good. If it is bright and does not seem to be blinking then the transistor in the zerocross tail is shorted out.