An adapter for mounting electric units to be wired to an electric system comprises a hollow anchoring body (10) having an upper portion (17) with a hole (12) for the passage of a driving control (6), a lower portion (16) removably coupled with the upper portion (17), a pair of reciprocally opposite side faces (15) at least partially open to allow the wires to access to electric units (2) housed into the anchoring body (10), means (14) for removably mounting the anchoring body (10) to a support (R), first holding means (27) adapted to removably fix the electric unit (2) to the bottom wall (13) of the lower portion (16). The first holding means (27) comprise at least one first and one second recesses (29) formed in the bottom wall (13) at respective open side faces (15) to house and snap-hold the electric unit (2).