The EtherRain controller replaces your current controller.
The valve wires are attached to the EtherRain controller just like they are with a standard timer box. A wiring diagram is included with the controller and the top label provides connection information.
Click Here for a connection guide for EtherRain 8.
Click Here for a connection guide for EtherRain 7P
EtherRain provides a gound connection for each valve, however in normal use only one or two ground wires are typically used. The ground wire, also referred to as a "common" can be attached to any of the provided ground terminals.
Also, as a side note. EtherRain contains a rain sensor input. This two terminal input is located between the two 8 position valve wire connector blocks. Be careful not to plug the power input into the rain sensor input.
Always work with the power off. Check your connector plugs before applying the 24 VAC power taking care mainly to check that the 24VAC power plug is plugged into the power connector and not the rain sensor input.