A Front End Module (FEM) assembly and associated assembly method with a rail system to enable efficient assembly, tighter clearances between the front end module assembly and the vehicle, and time and cost savings. The present disclosure provides a FEM assembly including grilles and headlamps and a rail system enabling the FEM to be assembled on a vehicle. Advantageously, the present disclosure allows the FEM to pass between fenders on the vehicle with a very tight clearance condition. The rail system included in the present disclosure allows the FEM to be assembled efficiently while protecting grilles and headlamps from being damaged by fenders and protecting the fenders from damage from the FEM.