In two-Higgs doublet extensions of the Standard Model, flavor-changing neutral current constraints can be addressed by introducing a $U(1{)}^{\prime }$ gauge symmetry, under which the Higgs doublets carry different charges. That scenario implies the presence of a $H^{\pm }{W}^{\mp }{Z}^{\prime }$ vertex at tree level. For the light “dark” $Z$ model ($Z^{\prime }=Z_d$) with $m_{Z_d}<10\mathrm{GeV}$, such a coupling leads to the dominant decay mode $H^{\pm }\to W^{\pm }+Z_d$ (for $m_{H^{\pm }}\lesssim 175\mathrm{GeV}$), rather than the usual type I model decay $H^{\pm }\to {\tau }^{\pm }\nu$, for a broad range of parameters. We find that current analyses do not place significant bounds on this scenario. Over much of the parameter space considered, the decay of a pair-produced $t$ ($\overline{t}$) into $H^{+}b$ ($H^{-}\overline{b}$) provides the dominant $H^{\pm }$ production. Analysis of available LHC data can likely cover significant ranges of our parameters, if $Z_d\to {\mu }^{+}{\mu }^{-}$ has a branching ratio of $\sim 20\%$. If the $Z_d$ decays mainly invisibly then probing the entire relevant parameter space would likely require additional data from future LHC runs. We briefly discuss the phenomenology for $m_{H^{\pm }}\gtrsim 175\mathrm{GeV}$.

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