When connecting the second CY-12C-T crash pad to the TD-17, be sure to use the V-Drums cable that is included with the VAD307, and connect the output of the CY-12C-T 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-307 cymbal pads:
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.
Connect the RDB cable to the BELL output on the CY-14R-T ride pad.
Connect the RD cable to the BOW/EDGE output on the CY-14R-T.
Crash Pad 1 (CY-12C-T):
Connect the CR1 cable on the harness to the CY-12C-T.
Crash Pad 2 (CY-12C-T):
Using the separate included V-Drums cable, connect the right-angle side to the output on the CY-12C-T. Connect its opposite (straight) end to the CRASH 2 input on the back panel of the TD-17.