Troubleshooting trim position indicator problems

[Dave M.]

Mine is currently broken, indicates full up all the time. It was previously intermittent, before that it was good. So here are some things I am doing to try and determine where the problem is.

First, I unmounted and laid down on the dash the gauge panel, so I can get to the back side of the instruments. Then I disconnected the wire at the trim indicator gauge that goes to the lower unit. I measured the resistance from this wire to ground, using the ground strap that crosses the back of most of the instruments as the ground reference.

A good reading would be between a few and around 150 ohms, depending on the position of the outdrive. Low ohms is drive down, 150 ohms or so is drive up. Mine measued open, so no connection to any sender, or the sender is open.

The boat is out in my garage, so I can easily get to the lower unit. I turned the wheel to the left for access, and removed the four screws that hold the plastic cover over the trim sender unit. I did not loosen the two adjusting screws. Then I popped of the plastic cover, being careful not to lose the o-ring that lays in a slot in the cover.



This exposed the sending unit ceramic board, and the two electical connecting screws behind the board. These screws hold the wipers make electrical contact with strips on the top and bottom parts of the ceramic circular board. So you can make electrical tests from these screws. The trim gauge is still disconnected at the dash so it will not enter into these readings.

First, I verified that one of them was ground by measuring from each to the one of the position adjusting screws I had no loosened. Sure enough, the top one measured less than an ohm to the outdrive.

Next, I moved on to the bottom screw. I measured from it to the outdrive at the adjusting screw again. This time I measured about 48 ohms. The drive is set roughly parallel to the keel, so this is about right.



This tells me that either the outdrive itself is not connected to the boats ground (not likely), or the wire from the sender to the dash is open somewhere (much more likely).

At this point I have not decided where to do the next check. It needs to be somewhere along the wire from the outdrive to the dash, and I need to check its resistance to ground with the wire at the dash disconnected from the trim gauge.

This thread belongs in the electrical section.

 

[Dave M.]

If the above test had failed, which it did a couple of years ago, then I would have needed to pull the ceramic disk out and check what is wrong. When you pull out the ceramic disk, what you have left is the mount, with two sets of wiper fingers. In mine, the top set of fingers connects to the boat ground, or battery negative. The bottom set of wipers connects to the input of the trim indicator on the dash, if all is well.



So you could just measure from the top wiper screw to the top adjusting screw, which I already did in the test above, but with the disc in place.

Then you can also measure from the bottom wiper mounting screw to the helm gauge, but that is a long run for the DMM.

When you pull off the ceramic disk, then you can measure the resistor on the back side. You should measure between the two silver end pads, it should read about the same as you see here. The first time mine broke, this reading was much higher and flaky.




Then you can also measure the conductor as it crosses from one end of the resistor under the plastic, and to the large wiper area on the other side of the disk.




You should get close to zero ohms, you are really measuring just the contact resistance of the probes. It is a bit hard to see in the above photos that the measurements are being taken on metallic plated areas. Here is a better view.



My original one failed because the resistor, which is probably silk screened ink, did not overlay properly on the metal deposition. This happened at the right end of the resistive paint. In the photo below you can clearly see that it does overlay on the left side. The picture is not good enough to check the right side. But you can also see three registration marks that the manufacturer uses to line up and check the silk screened ink layer with respect to the metal underneath. You should not accept a new part where these are not aligned, as it will likely fail like mine did.



The black ink layer must overlay the metal in order to have good electrical contact between the resistor and the end metal. If they just barely touch, then expect problems. The left end, where you can clearly see it, does not really matter, as the metal does not connect to anything else. But on the right end, it does. The metal crosses under the plastic over to the other half of the disk, where the top wipers make contact with it.

 

[DavidS]

Excelent Post Sir. You responded to my original post concerning this issue. I am going to hand mine back to the mechanic since he should stand behind his work but your info & pictures are excelent. The boat was in warranty when I turned in the work order for him to fix it or I would have tried the diagnosis my self. With your post I think I could have managed it.

Thanks...

 

[Dave M.]

I expect to post more on this as I work through the problem with mine. But right now I am packing the 5th wheel for a trip to the southwest. I hope to leave tomorrow or saturday, and be gone for two weeks. So I really don't expect to get more testing done until I get back.

Things I want to document are:

Where are the connections between the sender and the gauge that might fail, and where I might test back towards the sender.

What voltage normally comes out of the gauge when it is open circuited towards the sender, and when it is loaded with the sender. That should enable a quick check of the condition of the gauge.

I know that there is a connector up under tha dash the connects wires from the dash headed towards the bilge. I may have that diagram on line under the mid-270 DA thread. Maybe I am wrong. I am sure I have the breaker panel diagram, and the helm switch panel diagram. May not have an instrument cluster diagram.

 

[capz]

when you guys took off the trim sender did you notice how far the hinge pin was set in? The only thing keeping my boat from hitting water is the sender problem. Electrical is fine. It seems like the hinge pin is set in too deep. So the teeth on the pin don't always grab the teeth on the retainer when trimming. Going crazy on this thing. Spent hours trying to get it to work right.

 

[DavidS]

My pin was loose just enough to mess up the contact too. The mechanic tightened it with a tool he made from two nuts and a bolt. It took him a while to figure out why it would not work.