The adsorption behaviour of benzyldimethylphenylammonium chloride (BDMPAC) on polycrystalline gold has been investigated by means of dc (cyclic voltammetry) and ac electrochemical techniques (differential capacitance (DC), electrochemical impedance spectroscopy) and in-situ vibrational spectroscopy (surface enhanced Raman spectroscopy (SERS)). The adsorption of this quaternary ammonium salt is found to be mediated by specifically adsorbed chloride ions in the potential domain positive to the pzc; when chloride ions are expelled from the compact layer out of electrostatic reasons, BDMPAC adsorbs interacting directly with the metal surface through one of its aromatic rings. In accordance with the DC results, SERS show a reorientation of the molecule around -200 mV versus Ag/AgCl.