Chamberlain GS400D Owner's Manual page 22

MOUNT CONTROL BOX
4
Secure control box to mounting surface (post, wall,
column, etc.) using appropriate hardware (not
provided).
Square
Gate Post
Screw
INSTALL CONTROL BOARD
5
Attach antenna. Reinstall batteries, control board,
alarm, and reset button.
Installation
Wall
Drywall
Anchor
22
Antenna
U-Bolt
(Not Provided)