The Terminator must be installed as part of a collective on any open Command Bus ports. A terminator is needed to connect the units regardless of the command bus cable.
HDRS-CBC-TM
$4.99 USD
A Terminator must be added if you have a HYDROS Control 4 and a HYDROS Control 3 connected to the open Command Bus Port on one of the units. If the power supply is connected to the HYDROS 4, connect the Terminator to the available port on HYDROS Control 3.