This is one of the big advantages to using D4P. ONLY NEED ONE CONTROL UNIT. Remember D4P control unit, which is included in the PLUS and STANDARD kits defaults to 8 channels (4 for front and 4 for rear). So for example you can install REAR kit and in the future expand its facility, riding in the front a EXTENDED kit, which includes only the sensors and wiring and adapters for mounting.
Also the same CONTROL UNIT features 2 inputs D4P Speakers (Front and Rear) and two inputs for Display. You should consider other solutions based in analog sensors, might require up to 4 different CONTROL UNITS to connect a system of sensors front and rear, as they use a 4 sensor unit for each side of the vehicle and an special CONTROL UNIT to stablish communication with the vehicle, also on each side of the vehicle.
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