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Thread: Blown Fuse on Merc 50HP 4 Stroke

  1. #1

    Blown Fuse on Merc 50HP 4 Stroke

    On Sunday tried out the 50HP Mercury motor just to ensure all was OK for an outing on Monday. Started OK then realised I did not have the water turned on to the rabbit ears, so stopped the engine after about 5 sec runtime.

    Turned the water on, then tried to start the motor again and it was dead, replaced the 20amp fuse and motor started OK, ran for a while. and shut the motor down.

    On the water on Monday at the dock, same problem no start so replaced the fuse.

    I now suspect its the voltage regulator and will do a battery voltage check on the motor when running and if its greater than 14.5 volt the reg is sus. I wonder how many volts the stator puts out to blow a 20amp fuse, however with the fuse blowing it probably saved my battery from being charged with XX volts.
    (Checking the battery voltage may not work because the fuse may blow, soon after start up, and checking the voltage on the live side of the fuse may not be accurate because the battery is not in circuit)

    The 50HP motor had not been used for some time, ditto the small 2 stroke Merc backup that started 2nd pull.

    Comments and other areas to check appreciated.

    Peter

  2. #2

    Re: Blown Fuse on Merc 50HP 4 Stroke

    Finding this fault was like (to me) finding why a modern 4x4 goes into limp mode with no faults codes... ie not the MAF sensor, not the XX sensor, Not the,....

    Anyway, proved it was not in the charging circuit, the starting circuit (started without using the key), so looked like it was in the cable to the key/controls. Pulled the cable joint that goes to the meters...Trim/RPM/Km perH and could start the motor with the key without blowing a fuse. Turns out that that the trim meter like the other 2 meters are held in position by a U clamps, the other 2 meters have cutouts in their U brackets near the power/electrical screws but the trim U did not and vibration moved the U bracket to short 2 electrical connections.

    Just a few trips on my new motor/meter install of around a year ago, caused the problem, glad that it happened on the Murray in calm conditions rather than choppy water in the gulf.

    Peter

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