Lathem LTR-RBR - Manual (Page 6)

Installing the LTR-RBR
To install the Remote Bell Ringer, simply set the hidden Address
Selector switch / jumpers to match the Master’s Programmed Address
(default = Code 65) and attach the Communication Cable wire-pair
(with proper polarity) and the low-voltage Power Pair to the Terminal
Block, then secure the cover-plate to the electrical box with four 6-32
FH screws.