Plug connectors in the automotive industry which contain contact points must fulfill high technical requirements. Under temperature fluctuations of up to 150 degrees, which can occur several times a day in extreme cases, they must ensure permanent tightness. This is necessary so that the contact points are kept away from liquids such as water or motor oil. If the tightness is lost, it is very likely that the function of the plug connection will be lost. These connectors are manufactured from short glass fiber reinforced polyamides (PA) using 2-component injection molding. The insert is currently being made from PA 6 and the overmolding from PA 6.6. In order to achieve a better tightness between the insert and the overmold, melt ribs are applied on the insert, which are intended to partially melt during the overmolding and additionally seal the connection. The aim of this thesis is to connect the influence of geometric parameters of the melt ribs with the tightness of the two components with the help of standardized test specimens and Design of Experiments (DoE’s). Both optical and mechanical tests are used for this. In addition, other possible influences on the tightness, such as the conditioning or annealing of the inserts as well as the use of other material combinations and the aging of the test specimens are examined. With the help of optical tests, significant geometrical parameters of the melt ribs to improve the tightness could be found. It is shown that mechanical tests are only of limited value on the tested specimens. It was also determined that the tightness of the connection between the insert and the overmold could be further improved by using a different material combination. In contrast, conditioning and annealing the inserts does not result in a significant improvement in the tightness. In addition, it must be taken into account that there may be delamination between the insert and the overmold in aged test specimens.