When connecting the second CY-12C crash to the TD-17, be sure to use the included V-Drums cable that came with the VAD-306, and connect the output of the CY-12C to the 1/4" CRASH 2 input on the back panel of the TD-17. Here is the proper setup for all of the VAD-306 cymbal pads:
Hihat:
Connect the HH cable on the harness to the TRIGGER OUT on the bottom of the VH-10 pad.
Connect the HHC cable on the harness to the control out on the VH-10's motion sensor.
Ride:
Connect the RDB cable to the BELL output on the CY-13R ride pad.
Connect the RD cable to the BOW/EDGE output on the CY-13R.
Crash Pad 1 (CY-12C):
Connect the CR1 cable on the harness to the CY-12C.
Crash Pad 2 (CY-12C):
Using the separate included V-Drums cable, connect the right-angle side to the output on the CY-12C.
Connect its opposite (straight) end to the CRASH 2 input on the back panel of the TD-17.