  We analyze the sensitivity of low-energy fundamental symmetry tests to
interactions mediated by doubly-charged scalars that arise in type-II seesaw
models of neutrino mass and their left-right symmetric extensions. We focus on
the next generation measurement of the parity-violating asymmetry in M{\o}ller
scattering planned by the MOLLER collaboration at Jefferson Laboratory. We
compare the MOLLER sensitivity to that of searches for charged lepton flavor
violation (CLFV) and neutrinoless double beta-decay ($0\nu\beta\beta$-decay) as
well as present and possible future high-energy collider probes. We show that
for the simplest type-II seesaw scenario, CLFV searches have the greatest
sensitivity. However, in a left-right symmetric extension where the scale of
parity-breaking is decoupled from the $SU(2)_R$-breaking scale, the MOLLER
experiment will provide a unique probe of scalar triplet interactions in the
right-handed sector for a doubly-charged scalar mass up to $\sim$ 10 TeV and
help elucidate the mechanism of $0\nu\beta\beta$-decay.
