I have a custom DB9 cable that uses pins 2,3 & 5. Can I use this for serial communication from the PC to the (W)CCU?
No. You will need a full 9-pin null cable, since the (W)CCU communication on multiple pins.
Details on the RS232 connector can be found in theInstallation and User Instructions manual for version 3.1x found on the DCN-NG software ISO.