Main Motor Electrical Interference

What should I do if I have electrical interference from my main motor?

Check your unit

Turn your depth sounder on without using any options or selections to see if the problem may be in the way the depth sounder was set up to operate.

Turn all features on Auto and/or set all options to Restore Defaults  using the Setup Menu tab.

If possible, test your unit on a friend's boat that has the same type of sonar (i.e. side imaging, down imaging, standard 2D sonar) or the same model number. This will indicate whether the problem is with the depth sounder, the installation of any accessories, or with other equipment on your boat. If the depth sounder still has the same problem on your friend's boat, return it along with a letter explaining the problem in detail. If the depth sounder works correctly on your friend's boat, proceed with the appropriate suggestions below.

  • Check your depth sounder for interference with the boat sitting still, with all electrical equipment and motor(s) off. This will eliminate any possible source of interference. If this corrects the problem, then the depth sounder is receiving electrical interference from your boat equipment.
  • To determine the piece of equipment that is interfering with your depth sounder; turn each piece of equipment back on individually, until the problem starts again. When the problem begins again, the last piece of equipment turned on is interfering with the depth sounder. Also try this with your Main Motor and Trolling Motor running at different speeds.
  • Route all depth sounder cables as far away as possible from the main motor and any electrical wires attached to the motor. This will help eliminate interference to the depth sounder.
  • Using an In-line fuse, connect your depth sounder directly to the battery. This may eliminate faulty electrical connections and electrical interference, which may be causing your problem.
  • Have your boat's grounding system inspected by qualified personnel. Your depth sounder may be trying to operate on a floating ground .
  • Connect your depth sounder to a battery that is not being charged by your main motor. If connecting to a trolling motor battery, make sure you use the battery that provides the 12-volt power on boats that have a 24 or 36 volt system.
  • Interference from your main motor can sometimes be eliminated by installing resistor-type spark plugs. Also, worn spark plugs have been known to cause interference with electrical equipment. Most new motors come from the factory with resistor-type spark plugs installed, so have qualified personnel check for the type and wear on your spark plugs before installing a new set.
  • Unplug the tachometer, preferably at the motor. This will help eliminate interference being coupled into your depth sounder by the main motor through the tachometer.
  • An electrically noisy battery charging system on your boat's motor can also cause interference. Have this specifically checked for by qualified personnel.
  • Note: In those units that have a Filter, confirm that this is turned ON.  

If you are still having problems after trying the preceding suggestions, please Contact Humminbird Customer Service

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