Operating Instructions and Installation Instructions

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Sonar unit with external temp sensor, external speed sensor, or combo
speed/temp sensor. The primary temperature sensor is built
into the transducer.
Optional Speed Sensor Installation
All the units in this series can display speed and distance traveled, but
only the SeaFinder 640c DF comes packed with a speed sensor. If you
wish to purchase an optional additional sensor for your unit, refer to
the accessory ordering information inside the back cover of this man-
ual. The following instructions describe how to install the speed sensor.
Power/trans-
Speed sensor or
combo speed/
temp sensor.
Sonar unit rear view
Temp
sensor
Temp sensor built
into transducer.
Power/transducer
cable
3-amp fuse
Power/transducer socket
Accessory
socket