Several of the next generation instruments require high-resolution visible or infrared focal plane arrays that can only be achieved by building large mosaics of individual detector arrays. A significant step towards enabling these mosaics has been the introduction of the SIDECAR ASIC by Teledyne Imaging Sensors, a single chip for generating biases and clocks to the image sensor, and for digitizing up to 36 sensor outputs. To support large detector mosaics, we have developed a new control electronics approach that operates up to 32 SIDECAR ASIC / HxRG detectors in parallel. Important properties of the electronics include separately programmable voltage supplies for each ASIC with programmable over-current and over-voltage protection, synchronized operation of all ASICs, and support for post-processing of science data like co-adding of frames, sample-up-the-ramp processing, or centroiding. All ASIC and detector modes are supported, including window/guide mode operation. The electronics uses a full mode CameraLink interface to provide 680 MBytes/s of sustained bandwidth. In this paper, we present an overview of the electronics architecture, including the general computer infrastructure for data acquisition, storage and sharing. We will discuss benefits and features of the chosen approach, and present data captured using a SIDECAR ASIC and H2RG detector. The effort was funded by NASA's WFIRST project as part of an initial technology demonstration for large space-based detector mosaics.