An assembly device of an electric connector inside a lighting device of a vehicle, the assembly device being configured to carry out a mechanical and electric connection of the electric connector in a reception seat for the same, arranged within the lighting device and through an access hole obtained in a lateral wall of the lighting device; characterised in that it comprises: i)- a retaining and aligning support for the electric connector; and ii)- a command lever coupled in an oscillating manner to the support; iii)- the support comprising: an annular base configured to be coupled, in use, to the access hole; a fork configured to receive the electric connector in a sliding manner, the fork being arranged radially inside the annular base and being defined by a pair of first uprights arranged facing side by side one another and extending in a cantilever fashion in an axial direction from a first face of the annular base configured to be facing, in use, the access hole; and a pair of second uprights, that extend in a cantilever fashion in an axial direction from a second face of the annular base opposite the first face and are hingedly coupled to the command lever; iv)- the command lever comprising a first fork-shaped end, configured to engage, by snapping, the electric connector, an intermediate portion provided with hinge coupling means to the pair of second uprights, and a second end, opposite the first, configured as a handle for an operator; v)- the first end of the command lever being assembled in an oscillating manner inside a radial channel delimited by first uprights and shaped to receive, in use, said electric connector, the first end of the command lever being mobile between a first and a second opposite end (27,28) of the radial channel after a rotation of the command lever on said hinge coupling means, respectively between a first and a second end of stroke position of the command lever. i)- a retaining and aligning support for the electric connector; and ii)- a command lever coupled in an oscillating manner to the support; iii)- the support comprising: an annular base configured to be coupled, in use, to the access hole; a fork configured to receive the electric connector in a sliding manner, the fork being arranged radially inside the annular base and being defined by a pair of first uprights arranged facing side by side one another and extending in a cantilever fashion in an axial direction from a first face of the annular base configured to be facing, in use, the access hole; and a pair of second uprights, that extend in a cantilever fashion in an axial direction from a second face of the annular base opposite the first face and are hingedly coupled to the command lever; iv)- the command lever comprising a first fork-shaped end, configured to engage, by snapping, the electric connector, an intermediate portion provided with hinge coupling means to the pair of second uprights, and a second end, opposite the first, configured as a handle for an operator; v)- the first end of the command lever being assembled in an oscillating manner inside a radial channel delimited by first uprights and shaped to receive, in use, said electric connector, the first end of the command lever being mobile between a first and a second opposite end (27,28) of the radial channel after a rotation of the command lever on said hinge coupling means, respectively between a first and a second end of stroke position of the command lever.