In the context of the Standard Model we extend the S--matrix pinch technique for non--conserved currents to the case of three boson vertices. We outline in detail how effective gauge invariant three boson vertices can be constructed, with all three incoming momenta {\it off--shell}. Explicit closed expressions for the vertices γW−W+, ZW−W+, and χW−W+ are reported. The three boson vertices so constructed satisfy naive QED--like Ward identities which relate them to the gauge invariant gauge boson self--energies previously constructed by the same method. The derivation of the aforementioned Ward identities relies on the sole requirement of complete gauge invariance of the S--matrix element considered; in particular, no knowledge of the explicit closed form of the three boson vertices involved is necessary.The validity of one of these Ward identities is demonstrated explicitly, through a detailed diagrammatic one-loop analysis, in the context of three different gauges.