Mercruiser 5.7 with ALPHA trim gauge issues - Moves straight from up to down

[Jesterarts]

Hi everyone,

So I recently picked up a '96 Searay 210.

Overall great condition but there where a few things that needed addressing, one of them being a non-functional trim guage.

Inspection of the sender revealed that the wire going into the uni was worn and the wires exposed and corroded. So I picked up a new sierra unit, wired it up and installed it.

However, something is still not quite right.

The gauge now pretty much jumps straight from down straight to up. There isn't any inbetween. I haven't found any material on the internet where someone has talked about a similar issue.

Any thoughts?

 

[Bt Doctur]

the puck should have T.S. printed on the shell and there is an index mark you line up before you insert it into the hinge pin

 

[Bt Doctur]

does this help

 

[Jesterarts]

Yeah, I've followed the instructions for installing and nothing.

I've been doing some testing with the puck out to try and work out what is going on.

In a nutshell, I align the marks and then slowly rotate the puck clockwise as per the instructions to try and get the gauge to move to the 'down' positions.

Nothing happens which he gauge for about 90 degrees of rotation and then suddenly the gauge moves straight from 'up' to 1/4 from 'down'. Then I have indication for that last 1/4.

The thing is, this is ALL I get even through a full 180 rotation of the sender. If it was out of adjustment I would get the full gauge movement at some point.

What I am thinking is this. The 'UP' position is registering when I move the sender to a position where the contacts inside are not touching thus I get complete resistance in the form of a broken circuit.

This means, that the gauge is only registering between DN and 1/4 up.

Since getting to DN is the least resistance, I assume that there isn't an issue with the sender wire in terms of corrosion or the like as otherwise the gauge would never reach DN since resistance through the wire would always be high.

Also, the indication that I am getting between DN and 1/4 is WAY outside of what the sender positions should be to be indicating that position.

For some reason, it seems that the gauge is registering a LOWER resistance than it should as the sender is in a position between 3/4 and UP while the gauge is showing between DN and 1/4.

One piece of the puzzle that I am missing is IF the gauge uses the GRD wire from as a base line and measures the resistance DIFFERENCE between it's GRD and the signal is sends to the sender.

Then, if the GRD from the gauge is corroded, the resistance in it would be higher and the resistance difference between the GRD and the upper limit of the sender would ne LOWER thus the gauge would be reading at the lower end of the gauge.

If what I have written is correct and not total rubbish, then running the GRD from the gauge straight to the (-) on the battery should have the gauge working properly.

Unfortunately I won't get a chance to try this until next weekend. So now a week of waiting and pondering...

 

[Jesterarts]

Ok, just tried my theory and no cigar.

I discovered that the trim gauge still functions even without the ground at the gauge connected!

All in all the symptom I am having is like the sender unit is not generating enough resistance to register correctly on the gauge.

I decided to eliminate the wiring and the new sender unit.

First, I wired up the new unit straight off the gauge eliminating any loom issues. No change in behaviour from the gauge.

Then, I grabbed the old sender, wired that up to the gauge and same behaviour. So eliminating the new unit as a potential cause.

Finally, I plugged a multimeter into the wire AFTER the sender unit and connected to a good ground. Nice smooth increase in resistance though I didn't trust the reading in terms of measurement as I am not that great with using the tool.

I then spend some time studying the behaviour since I was much closed to the gauge than before when I was watching from the back of the boat.

I noticed that in turning the sender knob, I was able to get the gauge to pegg below DN, then slowly climb to just under the 1/4 mark before it pegged to UP. I opened the sender and the reason for it pegging to up was that I had moved the the sender to outside of it's contact range.

I'm thinking about trying to put a in-line resistor in the (S) wire and see if I can adjust that to the system works. It's like the sender is working between say 0 and 50 ohms while the gauge is expecting 30 to 100 or something.

Could this be a faulty gauge?

 

[Fishermark]

This may be obvious... I apologize in advance. But you do realize there are two pucks, right? One is a simple on / off. The other is a variable resister. From your description it almost sounds like you are working with the trim limit puck, and not the trim position puck. Is that possible?

 

[Jesterarts]

I thought that for a moment too. But I took apart the sender even just in case for whatever reason the cover was labeled wrong. But I am working with the correct one.

I've don't some further research and the Mercruiser senders should be putting out between 10 and 167 Ohm through their cycle. So I will have to grab a decent multimeter and check what range this one s putting out.

That should give me a fairly accurate indication confirming if the gauge is toast or if I have to dig deeper.

 

[alldodge]

I thought that for a moment too. But I took apart the sender even just in case for whatever reason the cover was labeled wrong. But I am working with the correct one.

I've don't some further research and the Mercruiser senders should be putting out between 10 and 167 Ohm through their cycle. So I will have to grab a decent multimeter and check what range this one s putting out.

That should give me a fairly accurate indication confirming if the gauge is toast or if I have to dig deeper.

To add to Fisher response, have you checked the wiring? One lead goes to ground (Black) and the other goes to a Brown/White stripe wire

 

[Jesterarts]

Yeah, wires are all good.

I've tested that I get correct voltage all along the line.

I also eliminated this being a wiring issue as I hooked up the sender at the gauge under the dash. So with brand new wires only 20cm or so long and the behavior on the gauge was the same.

 

[alldodge]

Sorry not asking if the wires are good, was asking if the color of the wire connecting to the gauge is the correct color, Brown with White stripe

 

[Jesterarts]

Correct wires are used. Brown/White to sender and black from sender to ground.

Also, as I mentioned, I eliminated the wiring as a factor in any case regardless of what colour they are at the back of the boat but connecting the sender directly to the gauge. Gauge in one hand, sender in the other, wires in between.

Same behavior.

 

[alldodge]

Ok, just tried my theory and no cigar.

I discovered that the trim gauge still functions even without the ground at the gauge connected!

All in all the symptom I am having is like the sender unit is not generating enough resistance to register correctly on the gauge.

I decided to eliminate the wiring and the new sender unit.

First, I wired up the new unit straight off the gauge eliminating any loom issues. No change in behaviour from the gauge.

Then, I grabbed the old sender, wired that up to the gauge and same behaviour. So eliminating the new unit as a potential cause.

Finally, I plugged a multimeter into the wire AFTER the sender unit and connected to a good ground. Nice smooth increase in resistance though I didn't trust the reading in terms of measurement as I am not that great with using the tool.

I then spend some time studying the behaviour since I was much closed to the gauge than before when I was watching from the back of the boat.

I noticed that in turning the sender knob, I was able to get the gauge to pegg below DN, then slowly climb to just under the 1/4 mark before it pegged to UP. I opened the sender and the reason for it pegging to up was that I had moved the the sender to outside of it's contact range.

I'm thinking about trying to put a in-line resistor in the (S) wire and see if I can adjust that to the system works. It's like the sender is working between say 0 and 50 ohms while the gauge is expecting 30 to 100 or something.

Could this be a faulty gauge?

To recap, The trim switch can be pushed and the drive comes up and stops at the preset limit. The trim gauge wiring is correct, sender is the correct one, yet the gauge jumps from full down to full up. Many boats suffer from bad grounding behind the helm (dash). Connect a wire from the negative battery to the ground terminal on the gauge. If after this connection it still does not function correctly, and you have 12V at then positive terminal of the gauge, then the only thing left is the gauge it self

 

[Jesterarts]

Thought I would give an update on this.

It was the gauge as I purchased a replacement (cheap one though) and I now get a reading.

Things I learnt along the way:

1. There are difference gauges for inboard and outboard application. I didn't know this and it was not called out in the ad for the gauge I purchased, therefore I had to install the gauge up side down as it read backwards. Needle goes up as the leg goes down.
2. I got a gauge that has an operating range of 0-190. What I didn't consider is that the factory gauge has an operating range of 10-160 including the 'trailer' function so I only see about 1/4 travel in the needled. However this is enough for the time.

Thanks for the help with this one guys.