To connect pads to the TD-50/50X sound module, we recommend the Roland PCS V-Drums trigger cables:
Roland - PCS-5-TRA | V-Drums Trigger Cable
They are available in three lengths and can be ordered through most all Roland retailers/distributors.
5 ft./1.5 m (PCS-5-TRA)
10 ft./3 m (PCS-10-TRA)
15 ft./4.5m (PCS-15-TRA)
Note: For the digital pads (VH-14D, PD-140DS, CY-18DR), use the Roland USB extension cables which are included in each box. If you need a replacement USB digital cable, the Roland Part number is 5100050611.