A light modulator includes a light guide to guide light by total internal reflection, a diffraction grating at a surface of the light guide, and a liquid crystal in contact with the diffraction grating. Embodiments use one or more specially designed test memory cells fabricated with direct electrical connections between the two electrodes of the cell and external contact pads on the surface of the wafer. In response to a difference in the first and second voltages an output representative of a ground fault in that wireline segment is generated. Subsequently, a representative of the business obtains authorization from the prospective client to provide information about products and services of the business.