  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 $\gamma W^- W^+$, $Z W^- W^+$, and $\chi W^- W^+$ 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.
