A waterproof electrical connector assembly releasably connects an electrical cable to a second cable, or to one or more electrodes or sensors in a housing that has a bore therethrough that accommodates the electrical cable on one end and a fitting on the other end. The fitting holds one or more electrodes/sensors in a bore through the fitting. The fitting is a commercially-available male-threaded polymeric fitting of the type used in High-performance Liquid Chromatography (HPLC) applications. This type of polymeric fitting has a conical, or tapered, ferrule portion at one end that is configured to fit securely into a female-threaded and chamfered bore in the housing so that when the fitting is tightened against the chamfered housing bore it forms a watertight seal which is waterproof to at least 10,000 psi. As the seal is formed, the components contact each other to form an electrical connection, illustratively, a connection from electrode or sensor probes to the cable leading to measuring equipment.