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Old 10-03-2020, 15:40   #1
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Join Date: Mar 2020
Location: Marco Island, FL
Boat: Catalina Morgan 381
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First time owner - help with new Water tank monitor

Greetings All! My first post. I have been lurking for years and finally got a boat and now -surprise- need some help and advice.

I have searched previous threads with no luck. Maybe my question is super basic and hopefully someone has an answer that can help me!

This is on a 1993 Catalina Morgan 381

The old monitor had a broken needle. The previous owner purchased a new monitor panel that matches the old one (but much newer model), but never installed it. Looks to be a generic made in China sort of thing.

Here is the meat of my issue:
-Each tank appears to have a sensor on the top of the tank with two wires - one black and one white going into a larger grey sheath together to route through the boat.
-When I removed the old monitor, it had three wires connected to each of the sensor locations on the monitor - a single white wire for each tank.
-I connected the power to the new monitor (it works) and connected the one white wire to the corresponding tank number.
-None of the tank monitors are showing up or moving the analogue needle.
-Nothing is labeled behind the nav station.
-There are no other obvious black wires or a grey sheath to match what there is on the tank side to match what comes out of the nav station.
-The instructions on the new monitor show only one wire to connect to from each tank.

Here is my question:
-If there are two wires coming out of the each tank sensor itself, should I be looking for another wire somewhere to correspond to the other respective
black wire from each tank sensor?
-Is that wire a ground wire that they all share perhaps?
-I found a stray black wire behind the nav station near the monitor that is missing one side of a butt connector and am wondering if I simply need to connect that potential ground wire to the tank monitor ground wire.
-Also new to using a multimeter - is there a way to use a multimeter to determine if the wire out of the tank is the same wire in the nav station? (my next forum search)

Hope this spells it out and hope I am on the right track. I am familiar and comfortable working with electrical but probably only enough to get me in trouble. I do know to turn off the monitor 12v power while working with the wires. Since nothing is labeled I am hesitant to just go connecting things - could end in disaster.


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Old 10-03-2020, 18:19   #2
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Re: First time owner - help with new Water tank monitor

Glad you decided to come out of the lurker closet and become a poster...welcome aboard!

From your description it appears to be a Wema gauge. Instead of trying to sort out what goes where, I'd just replace the whole thing (you can leave the sender unit in place) with a system that uses a sender that goes on the OUTside of the tank. This is the one I recommend...the "solo" is the single tank monitor Scad Tank Monitors If your existing system is a Wema, you will have to run new wiring, but it's not a difficult job.


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Old 10-03-2020, 19:01   #3
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Re: First time owner - help with new Water tank monitor

Or consider a TankTender. Pneumatic, not electrical at all. Extremely accurate and reliable, plus a nice company to work with.

just a happy customer
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Old 11-03-2020, 02:06   #4
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Re: First time owner - help with new Water tank monitor

Greetings and welcome aboard the CF, Believe.

In this diagram, the common negative is labeled ‘Yellow”, the Senders are “Blue, Tan, or Pink”, and the positive feed is "Violet”.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 11-03-2020, 11:33   #5
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Re: First time owner - help with new Water tank monitor

Welcome to the brotherhood of maintenance and repair, it will teach you patience, or how to spend your money, depending on the outcome.

Any circuit has to have a path out and a path back for the current to travel over in order to drive a gauge. If a sensor has only one wire, it is relying on the tank, or engine to be the "ground" or return path. If you have three or four wires between the gage and the sensor, you may have a powered transmitter or even a digital sensor, which is harder to troubleshoot.

For two wire systems, you always have the option of adding an additional wire from the instrument to the sensor, rather than relying on the tank to be the ground path. Ground wires or bonding wire often suffer from corrosion. Since they are hidden or not obvious, they don't receive any TLC when systems are cleaned up. If you have a bad or broken ground, you will not have a reliable gage.

When I got my boat, it had a stud on the engine that had a lot of ground wires all coming to that stud. It seemed as if every system's ground came back to that single point. This is not good. It is hard to troubleshoot and you have half of each system on a dirty and vibrating piece of equipment. I am a fan of one or more ground bus bars which provides many screw terminals along a common bar. This way, each ground wire can be individually tightened down and labeled. The bar ties all the grounds together and makes testing the grounds easy.

A multimeter can diagnose your system. You may need some extension wires and aligator clips to extend the reach of the multimeter's test leads, but if you measure resistance between the guage's ground terminal and the sensor housing it should read very close to zero ohms. If it reads fairly high, you have a corroded ground system. This could be the ground wire turning to green powder, or corrosion at the mounting terminal on the tank, guage or somewhere in-between. Corroded crimps on the wire terminations can also pose a problem. If the multimeter reads infinite resistance, the ground is non-existent. Then you need to either clean the existing ground system, or install a new wire.

Wiring on a boat is not like wiring in a house. You should consider inspection of your wiring part of your annual maintenance, with wires being replaced as needed. My advice when replacing wiring or installing new systems is to take the time to remove the old wiring. There is nothing more frustrating than trying to diagnose a problem with 20 odd wires in the bundle that aren't being used any longer.

Bad crimps on the wire ends are very common. They don't normally reveal themselves initially, but since the wiring is not fully compressed by the ferrule, corrosion and intermittent connections can start inside the fitting. This only gets worse over time, from continued corrosion and the small amount of arcing as the circuit makes and breaks. Testing the wire ends can be hard. If you move the wire, you may re-establish the connection momentarily and get a good reading.

If it is a critical system, and I got a bad reading, I start with a visual inspection. If I don't like what I see, I just replace the wires.

If the crimp looks suspect, but the wire looks fine, I cut off the wire end and crimp on a new one.

If when I cut off the old wire end, the wire itself looks green, I replace the wire immediately. Green wire is stiff and brittle. It can turn to powder inside the insulation jacket. Depending on what the circuit does, this can be dangerous.

Your multimeter can also be used to test the sensor itself. Most two wire sensors either vary the resistance or capacitance that the circuit sees. If you put your multimeter across the sensor contacts (when it is not wired into the system) you can make a determination as to whether the sensor is good or bad. Most maintenance manuals will tell you what results to expect.

Good luck,
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Old 11-03-2020, 15:20   #6
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Re: First time owner - help with new Water tank monitor

Or, forget all this electric nonsense and complexity. Drill a hole in the top of the tanks and epoxy a bronze plug like they have for drains on wooden dinghy transoms. Use a wooden dowel and dip it. A pencil mark for the level. Dowel stays under cushions for ready use. I always do this on any boat I've owned. Never trust any of this other rubbish!!! In mid ocean your water is your life. This world has gone crazy. What happened to simplicity??? Sorry for the rant.
I drive a 90's Japanese car for the same reason.
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Old 11-03-2020, 15:45   #7
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Re: First time owner - help with new Water tank monitor

I have an antique airplane that uses a cork with a wire which pokes out of the gas cap. Simple and reliable. Love it.


He asked how to troubleshoot it.

Give him a fish or teach him how to fish...

I may borrow your tank gage idea for my own boat on the water tanks. I'm thinking of a tube with the cork and wire inside, so I don't have to stick anything in the tank, just unscrew the cap and let the wire pop up. After the reading, push the wire down and put the cap back on.

If I had a dowel, it would go missing.

Are you still using lead lines for depth?
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Old 11-03-2020, 16:05   #8
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Re: First time owner - help with new Water tank monitor

+1 on the tank tender-- expensive but the last one you will ever have to do.
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Old 11-03-2020, 17:06   #9
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Re: First time owner - help with new Water tank monitor

install a fitting to the top and bott of the tank and put a clear plastic tube in between so you can see water level at a glance
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Old 18-03-2020, 15:34   #10
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Re: First time owner - help with new Water tank monitor

Thanks so much for the welcome to the community and the advice! Diving in with a multimeter now. Will post my results that may someday help another sailor in need.

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monitor, water

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