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Bennett HPU Bad ?

fishy talesfishy tales Posts: 56 Greenhorn
How can I test my Bennett HPU to see if it is bad or not? I did all the troubleshooting I could and this is what I come up with. First checked the switch and its wiring making sure all connectors were good and tight with no corrosion. Then I reversed the lines from on side to the other on the HPU , doing that just reversed the problem to the other side. In doing what I have done I went and bought a soleniod (red) for the port side tab. After installation and testing, the situation was still the same.To the wire harness of the HPU I tested each prong with a jumper wire. Starboard and Port side soleniods seem to work right, with a loud clicking noise. Testing the other wires in the plug to run the motor one of them didn't seem to run as loud as the other and acted like it was struggling to run, Is this an indication that the HPU is bad?

Thank you for any help you may provide me.
:Rockon Maybe - Maybe Not --- Lets Find Out :Rockon


  • TabmanTabman Posts: 146 Deckhand
    Fishy Tales,

    Can you tell me how old your Trim Tabs are and what type of boat you have?

    Is only one side working? I think you might have a faulty switch.

    Here is a link to a video that covers how the system works and basic troubleshooting http://www.bennetttrimtabs.com/videoplayer.php?vID=10

    Here is a link to a video that covers one side not working http://www.bennetttrimtabs.com/videoplayer.php?vID=15

    Below you will find troubleshooting you can print and take to the boat Do step 3 and if the boat is older look at step 6.

    Let me know what you find and I will be happy to help.

    Bennett Marine

    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).
  • fishy talesfishy tales Posts: 56 Greenhorn
    Well I did all the testing I could. I tested the wires like explained in the troubleshooting guide and it still didn't work for me. This time I had some help and tested the plug at the HPU and with the switch. Everything seem to work correctly and with proper voltage of 12.7 except for the port side soleniod, no power. Traced the red wire through the boat and found it was broken in two. Not able to repair it yet as I need to get some spliceing material, but am sure that will do the trick.

    Thank you for your help.
    :Rockon Maybe - Maybe Not --- Lets Find Out :Rockon
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