This report is the last in a series that describes the preliminary design of an instrument capable of mapping conductive fractures deep below the surface of the earth. Earlier reports dealt with theoretical analysis, the general status of the instrument development, and materials vendor searches. Here, attention is focused on the electronics design and prototype hardware to perform the mapping task. A phase-sensitive detector is described that has sensitivity in the tens of nanovolts. Coil-switching circuitry is also described, as well as a downhole data link tailor-made for this particular instrument's needs