VTech IS7121 Installation Manual page 9

5.
Loosen the screws and the metallic plates, then slide the metal part
of the wires underneath the metallic plate as shown. Twist the screws
to secure.
Metallic
plate
Wire with
black end
If you already have a wired doorbell installed,
see Installing the doorbell with an existing
wired doorbell on pages 12 to 14 to install your
new IS7121 doorbell unit.

Screws
Metallic
plate
Wire with
red end