Intermittent Bennett Trim Tabs

I was having some issues with my boat planing when I first got her and narrowed it down to a couple of things including the trim tabs not going down. It seems sometimes they do and sometimes they dont when using the switch at the helm. If I jump the terminals at the pump, down in the lazarette, they always go down or up. I have taken the switch apart and cleaned the contacts but that doesn't seem to help. I ran a cord direct from the switch down to the terminal block and they worked perfectly but I couldn't live with that dangling down the bridge ladder and laying on the deck.

Before I left for a trip this weekend I let the tabs down at the dock before I left the house. When I got her wound up she planed perfectly and ran like a scalded dog. I was cruising at 17 knots running 1900 RPM which is the best I have seen so far. I pulled the tabs back up and when I headed home I ran the down button at the dock but never verified they were down. When coming back, with less water and fuel, she didn't want to plane as well and seemed to be struggling although we did have a significant following sea. Got home and sure enough the tabs did not go down nor would they operate at the dock using the proper switch.

Before I pull new wiring up to the switch I wanted to ask here if anyone has had similar issues and what their fix was. My first thought has always been the ground wire but it does not go up to the switch and when I jump the circuit to let them down I use the same ground source. When not operating I get proper voltage to the switch but I am thinking I am not getting enough amps.

The flat connects they use turn green quickly.

But more than probably, that f%$^ng negative lead to/on the pump motor has caused a few words from me, down in some bilges.

All the connections look good and it appears the terminal block has been replaced. I will double check the negative. I was thinking on this some more and remember the last time I played with this it would start working fine after I used the jumper. I am wondering if there is a voltage drop due to the long length of the wire to the bridge and if the tabs are sticking slightly. Going to play with it some more this week.

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Originally Posted by Briankinley2004

All the connections look good and it appears the terminal block has been replaced. I will double check the negative. I was thinking on this some more and remember the last time I played with this it would start working fine after I used the jumper. I am wondering if there is a voltage drop due to the long length of the wire to the bridge and if the tabs are sticking slightly. Going to play with it some more this week.

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you might be surprised how far corrosion can creep inside insulation of non tinned wire. enough to kill the circuit.

Update to the thread. Still no fix but found multiple issues today which I corrected. Someone prior had replaced some of the terminal ends and spiced some rather thin (estimated 16 ga) non-tinned wire onto the house wiring which appears to be 12 gauge for the main feed and 14 ga for the feed to the bridge. Below is a picture of what I repaired. The main feed had the positive wire scaled down to a 16 ga both where it went to the terminal block and a jumper that went to another terminal which feeds the bridge switch along with a splice in that wire that was too small. I cut these wires out and installed tinned 12 gauge wires and replaced part of the ground feed that had become hard right at the terminal. Following Cap Ralph's advice I removed the pump and checked the ground wire. Sure enough it was harder than a 4 hour erection with a diameter too small for the job. I replaced it with tinned copper as well. I just knew this would fix my issue but went to the bridge and no cigar. Jumped the wires out at the terminal block and it worked perfectly. I am thinking the issue is either with the supply wire to the bridge, the main positive or the ground as nothing works when I press the switches.I think my next move is to connect the supply to another circuit and if that doesn't work I will bypass the supply wire to bridge and see if that fixes it. If not I will be calling Bennett before I pull new wires to the bridge.

Attachment 73009

On the switch back is just the 12V lead and 4 wires, the 2 wires for each fluid solenoid and 2 wires for motor rotation. Tie the 12V to your volt meter positive probe, Tie your negative probe to a known good negative (ground) source. Your meter should read a good 13Vdc.
Now, touch the other 4 wires and note the voltage drop on the meter.
You should hear a click or the trim motor run (may take an extra set of ears).

This also bypasses the switch.
Don't think these ole switches last forever, they do mess up ...

So I finally got this fixed today. Thought I would post the solution in case others are having similar issues. I saw a post in some Internet forum where someone put Bennett's repair manual up. Went through all the troubleshooting there, much of which I had already done, and no cigar. I had noticed voltage dropping from. 13 to 10 when I pushed the switches so I hooked the supply directly to a separate 12 volt battery instead of the house battery but no luck. I went back to my original jumper straight from bridge terminal block to terminal block at pump. Worked fine no issues. So I bit the bullet and ran a single 12 gauge tinned wire to from the bilge supply to the bridge to power the switch. I had to take a different path than the main cable as it ran behind the electrical panels, however I made it work and added nomenclature. Hopefully this is a one off and wherever the issue is doesn't spread to the other wires in the same cable. A visual inspection, where possible, did not reveal any swollen or otherwise compromised areas on the outside of the cable.

As you get things sorted out the working tabs will help with cruise speed. Had mine on the hard with the tabs down where I leave them for cruise speed. They don't look like they are down enough to make that big of a difference but they do.

I have a related question. I am considering the new Bennitt auto trim switch. Has anyone tried the automatic switch? If so did you like the results and did you have to run any extra wires?

Funny, sometime mine don't work when I don't turn on the 32V breaker on for them. I hit the switch but nothing.