Raymarine L750 Operating Handbook page 33

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2. The 6-foot power cable supplied with the display unit should reach
the source of DC power. Connect the power leads directly to the
main battery isolation switch or breaker, or route the power leads to
the DC power distribution panel.
3. It is very important that you connect the power leads correctly. See
Fig. 2-18. In the power cable, there are several twisted pairs of small
wires which are not used in this application (orange, yellow, green
and blue insulation). You can clip off the ends of these small wires.
Only the large red and black wires are used to supply power to the
Fishfinder.
At the power source, connect the red wire to the positive terminal
(+), and the black wire to the negative terminal (-). The negative
terminal may also be called "ground" or "earth." (The display unit is
internally protected if you accidentally reverse the polarity of the
power wires.)
4. Attach the red or positive wire to a 5 amp circuit breaker. If the unit is
connected directly to the boat's battery, include a 2 amp in-line fuse.
(In-line fuses are available at most marine supply stores.)
5. To prevent any interference or electrical noise, separate the
Fishfinder power wiring as much as possible from other devices.
See the section on "EMC Installation Guidelines."
6. If you need to extend the power wiring by more than 10 feet, use a
larger wire size. This will allow the wires to deliver the correct voltage
in spite of the longer wire distance. For runs of 20 to 35 feet, use #14
AWG.
If you extend the power wiring, be sure all electrical connections are
solid and durable. Soldering is the best way to make these
connections. Insulate all connections using heat-shrink tubing or
electrical tape. You may also use crimp connectors or a terminal
strip, but be sure to use good-quality marine-grade parts.
7. At the rear of the display unit, plug in the power cable.
Note - Press firmly when inserting the power cable and transducer
cable to ensure a tight seal.
8. When you press the Power button, the display unit should turn on. If
the unit will not turn on and you suspect that you may have reversed
the power connections, check the DC power lines all the way back to
the battery. If the polarity is not correct, reconnect the leads properly
and try again.
L750 Fishfinder: Installation and Operation Handbook