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Tabman......V351 Pump Issues

I have a V351 pump that was operational but was very slow in responding and finally quit working all together. Part of the troubleshooting we did is take volt readings at the harness side leading from the switch. Here is what we found:
Left Down:
Red 9V
Green 12V
Yellow 11V
Blue 12V

Left Up:
Red 8.8V
Green 12V
Yellow 12V
Blue 9.8V

Right Down:
Red 12V
Green 10V
Yellow 10V
Blue 12V

Right Up:
Red 12V
Green 10V
Yellow 12V
Blue 10V

So it appears power is getting to the motor but there is no movement with the tabs and no sounds. There are no visible leaks but could low fluid levels cause the pump not to work?

Any suggestions/thoughts?


  • TabmanTabman Posts: 146 Deckhand
    How old is the pump? What type of boat?

    Some of the voltages are too low for it to work properly. Also the yellow and blue wires should not be having that much voltage at the same time.

    I would like you to do step 3 right behind the switch. And also right at the pump with the harness disconnected. Also look at step 6 and clean both ends of the ground wire at the pump.

    Let me know what you find,


    Fluid: Automatic Transmission Fluid (ATF) any type. Hydraulic Power Unit is self bleeding, running the Trim Tabs up and down 3-4 times will purge air from the system.

    Fuse: 12 volt system use 20 amp in-line fuse on positive. (24v & 32v use proportionately smaller)

    Red= Port Valve
    Green= Starboard Valve
    Blue=Motor Forward (pump pressure)
    Yellow= Motor Reverse (pump retract)
    Black on HPU=Ground
    Orange on Helm=Control Positive


    1.If one side is not operating reverse hydraulic lines on the front of the Hydraulic Power Unit to determine if the malfunction is in HPU or actuator / hydraulic lines. If after reversing the lines symptom shifts to the other side the malfunction may exist in HPU. If the symptom remains on the same side, malfunction may exist with the actuator / hydraulic lines

    2. Is the unit receiving a solid 12 volts? Low voltage will some times cause the solenoids to not open preventing the tabs from moving even though the pump motor is running.

    3. Conduct the following test:
    Remove the wires from the helm control and touch together as follows:
    Orange (+), blue, red= Port trim tab down
    Orange (+), blue, green=Starboard trim tab down
    Orange (+), blue, red, green= Both trim tabs down
    Orange (+), yellow, red= Port trim tab up
    Orange (+), yellow, green=Starboard trim tab up
    Orange (+), yellow, red, green= Both trim tabs up

    If the trim tabs function correctly for each wire grouping then the switch is at fault. Also note that any loose or missing screws on the back of the switch (whether a wire is connected there or not) can cause the pump to malfunction.

    This test may also be done right at the pump by substituting a "hot lead" for orange. There is usually a connector to the wire harness within a foot or so of the pump. You want to check this connection for corrosion. You may wish to cut the connector off on the pump side and try the test on bare wires.

    4. If you suspect corrosion on the wire connector near the pump, cut it out, test as above and reconnect using butt splices.

    5. If you conclude the problem is in the pump, contact me. Bennett Trim Tab Systems carry a five year warranty.

    6. Check to see if there is a relay in line on the wiring harness near the hydraulic power unit. If there is it is an Interrupter Relay (IR1000). It prevents the system fuse from blowing if you try to actuate one trim tab up and the other down at the same time. After you test as outlined above, try removing the relay from the wiring harness and retest the unit.(Note: the interrupter relay is no longer used in current Bennett Trim Tab systems and has been replaced with a Switches that "lock out" preventing a blown fuse).
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