Holding Tank Full light wiring

[Bill Root]

I need help understanding how the "holding tank full" lights on BUFFALO GAL are wired. This past weekend they all came on even though I know the tank is empty. I still have the original light/switch panel in each head.

I opened the access hatch above the holding tank and located what I believe is the tank level sending unit, since it's the only thing on top of the tank that doesn't have a large hose going into it, and it is in the location the boat drawings say it should be. However, the wiring diagram I have for the boat shows two wires going to the unit, one coming in from the breaker panel and the other going out to the guest head switch panel. Mine has only one large wire (not a copper tube) going into it. As soon as I touched the wire it broke off, but the tank lights remained on until I turned off the breaker. The wiring diagram that came with the boat is dated 4-18-85 and marked CT-103-ED, so I'm assuming they used the same wiring scheme for my 1988 54MY as they did for the 53 ED's.

I tried taking a picture of the sending unit, but because of the location I can't get a decent shot, so I'll attempt to describe it. There is a large octagonal shaped fitting that screws directly into the tank. A smaller square fitting screws into that one, then another even smaller fitting on top of that has a hole in one side that it appears the wire fits into. There are no other connections for wires on the unit. From the looks of it, I would say that it's probably original equipment.

Does the fact that the lights stayed on when the wire came off mean that the lights are activated when the circuit is broken? Kind of counter-intuitive, but I know that is how the systems monitor works. Does what I have sound familiar to anyone, and if so, can you shed some light on how this thing is wired? I can get a long without the lights, but they were certainly handy to have.

As always, any insights would be much appreciated.

 

[Nonchalant1]

Hi Bill,

The 1978 version was a simple pressure switch on a dip tube into the tank with a single wire. As the level in the holding tank rises, the liquid enters the bottom of the air filled dip tube and begins to compress the air. When the pressure gets high enough the switch makes the light go on. Given that your lights stayed on when the wire was broken off, it sounds like the switch is "normally closed" meaning it would pass current, so to turn the light on, it opens, meaning it will not pass current, and the sensor senses that and turns the light on. This would explain why a disconnected wire leaves the light on.

If the connection at the tank switch was so corroded that it fell off, maybe it just would not pass current to the switch, explaining why the light was on incorrectly. If so, maybe just clean up the connection and reconnect to see if that makes it work.

Doug

 

[Maynard Rupp]

On our '86 36C, the thing that comes out of the tank is a small black tube. If you follow that tube it ends at a thing that looks like a hockey puck. Inside that, ( the outside is just soft rubber that can be pulled off), is a small switch and an aneroid. As the tank fills, the aneroid expands and eventually closes the switch. One wire goes from the switch to ground and the other wire goes to the light. 12 volts is on the other side of the light, or lights, just waiting for that little switch to close and complete the circuit to ground. What happens inside the hockey puck is the lever that goes from the aneroid to the switch has a pivot about half way. (Think of a kid's teeter totter and you get that idea straight.) That arm is dicromated and tends to get a bit of corrosion at the pivot. Now, the aneroid moves the arm as your tank fills, the switch is made, you empty the tank, and the corroded arm never releases the switch. We were able to flood ours with WD 40 to free it up, spray a little lube or grease to keep it working, and re-assemble the thing. Ours has worked fine for the last 8 years.

 

[Boatnut]

Are you sure there is only one wire going to the sending unit, and not a multiconductor with 2 wires in it? Not seeing the unit, I can't figure how it would work with a single conductor going to it. If it has 2 leads going into it, trim them back, make sure they are not shorted together, turn on the power see what the lights do. Turn off the power and short the 2 wires together, turn on power, and see what the lights do. If the light come on and off, the the send is defective, or perhaps you can rewire the sender. Be cautious not shocks needed.

 

[Genesis]

Gigabite was very similar to Maynard's setup -- there was a tube that went to what amounted to aneroid chamber that was sealed and had a switch actuated by the diaphragm. I presume the inside tube was at 1/4 of the way down or thereabouts so it would build pressure once the level reached that point and then actuate.

 

[fissioneng]

Ditto, looks like the red puck in the upper left corner. Black tube comes out from underneath. I took the whole thing apart, repainted, lubricated, working great now for 4 years.

 

[Bill Root]

Hi Bill,

The 1978 version was a simple pressure switch on a dip tube into the tank with a single wire. As the level in the holding tank rises, the liquid enters the bottom of the air filled dip tube and begins to compress the air. When the pressure gets high enough the switch makes the light go on. Given that your lights stayed on when the wire was broken off, it sounds like the switch is "normally closed" meaning it would pass current, so to turn the light on, it opens, meaning it will not pass current, and the sensor senses that and turns the light on. This would explain why a disconnected wire leaves the light on.

If the connection at the tank switch was so corroded that it fell off, maybe it just would not pass current to the switch, explaining why the light was on incorrectly. If so, maybe just clean up the connection and reconnect to see if that makes it work.

Doug

Thanks, Doug. What you describe makes sense. It's how the systems monitor works. I hope the solution is that easy.

Bill

 

[Bill Root]

On our '86 36C, the thing that comes out of the tank is a small black tube. If you follow that tube it ends at a thing that looks like a hockey puck. Inside that, ( the outside is just soft rubber that can be pulled off), is a small switch and an aneroid. As the tank fills, the aneroid expands and eventually closes the switch. One wire goes from the switch to ground and the other wire goes to the light. 12 volts is on the other side of the light, or lights, just waiting for that little switch to close and complete the circuit to ground. What happens inside the hockey puck is the lever that goes from the aneroid to the switch has a pivot about half way. (Think of a kid's teeter totter and you get that idea straight.) That arm is dicromated and tends to get a bit of corrosion at the pivot. Now, the aneroid moves the arm as your tank fills, the switch is made, you empty the tank, and the corroded arm never releases the switch. We were able to flood ours with WD 40 to free it up, spray a little lube or grease to keep it working, and re-assemble the thing. Ours has worked fine for the last 8 years.

Thanks, Maynard. I'll check again to see if it's a tube coming out of the sender, but it definitiely looks like wire to me. Granted, it;s in a really bad spot and hard to get a real good look at.

Bill

 

[Bill Root]

Are you sure there is only one wire going to the sending unit, and not a multiconductor with 2 wires in it? Not seeing the unit, I can't figure how it would work with a single conductor going to it. If it has 2 leads going into it, trim them back, make sure they are not shorted together, turn on the power see what the lights do. Turn off the power and short the 2 wires together, turn on power, and see what the lights do. If the light come on and off, the the send is defective, or perhaps you can rewire the sender. Be cautious not shocks needed.

Definitely looks like only one wire, and there is only one place for a wire to be connected to the sender. Unless, of vourse, the connection is actually inside the sender and the wire going in is actually a multi conductor. I'll check that out when I'm back at the boat this weekend. thanks.

 

[Bill Root]

Gigabite was very similar to Maynard's setup -- there was a tube that went to what amounted to aneroid chamber that was sealed and had a switch actuated by the diaphragm. I presume the inside tube was at 1/4 of the way down or thereabouts so it would build pressure once the level reached that point and then actuate.

Thanks. I'll look again to be sure it's not a tube. It's in a bad spot, kind of back under the stairs going down to the companionway back to the staterooems, so it was difficult to get a really good look at it.

 

[Bill Root]

Ditto, looks like the red puck in the upper left corner. Black tube comes out from underneath. I took the whole thing apart, repainted, lubricated, working great now for 4 years.

Thanks for the photo. The tube looks very similar to the one in the photo, but I haven't seen anything like that red hockey puck. The wiring diagram shows something that might be it in the guest stateroom. I'll check when I get back to the boat this weekend.

 

[Angela]

There must be something in the air....

About 10 days ago, my light came on for one of my two tanks for the first time since I bought the boat a little over 6 years ago. I got up one night around 3AM wondering what that red glow was coming from under the door and was very surprised to find the light on. I checked the other head that shares that tank and it was on, too. I looked again the next morning to make sure I wasn't imaging that in a half-asleep stupor.

I moved to a new slip just down the pier a week ago, and just now got around pumping out that tank since I had to pry up the finger pier planks with a crowbar to get to the pump out in this slip. I'm not sure why the marina just planked over it so it couldn't be used. Well, the tank is empty, and the lights stay on. I guess I'll just remove the lamps - I never relied on that light anyway and had no idea it even worked. I want a set of gauges for the tanks that have a read out to tell me what their status is, rather than a sudden "full."

 

[SKYCHENEY]

Ang,

You can pull the fuse in your 32v panel. Once you open up the breaker panel, you will see a few fuses there. One of them is for the holding tanks.

Then you can put in a Hart Tank Tender. Mine is accurate to within a gallon or two.

 

[Maynard Rupp]

No Ang...Read my previous post. This is a very simple fix once you see it. A light bulb needs voltage and ground to light. That switch in the hockey puck just makes and breaks that ground like a light switch. The arm that operates that switch corodes a bit and the pivot gets stiff. When your holding tank fills, the switch lights the light or lights in your case. When you empty the holding tank, the lever sticks in the on position because of the corrosion. A little WD 40 and some manual operation to free it up and you are good for a long time. That red cover you see is soft and pliable rubber and is easily pulled off to reveal the problem. I am sure that you have moments when you are full of....Oh well, never mind, pull the bulbs if you must. You will never know when your tank is venting overboard and polluting the harbor if you just pull the bulbs. C'mon Ang...fix it right.

 

[SKYCHENEY]

No Ang...Read my previous post. This is a very simple fix once you see it. A light bulb needs voltage and ground to light. That switch in the hockey puck just makes and breaks that ground like a light switch. The arm that operates that switch corodes a bit and the pivot gets stiff. When your holding tank fills, the switch lights the light or lights in your case. When you empty the holding tank, the lever sticks in the on position because of the corrosion. A little WD 40 and some manual operation to free it up and you are good for a long time. That red cover you see is soft and pliable rubber and is easily pulled off to reveal the problem. I am sure that you have moments when you are full of....Oh well, never mind, pull the bulbs if you must. You will never know when your tank is venting overboard and polluting the harbor if you just pull the bulbs. C'mon Ang...fix it right.

But that little tube rots off in the tank and then the light doesn't come on until the tank is full/overfull. That system is just not that great. There are much better options out there now.

 

[TopHattandTails]

First tell tale sign that your approaching "full" is the smell. At 3/4 tank, my tanks start to fumigate a little. Time to pump out at that point. My Hart Tank Tender usually reads about 3/4 then.

 

[SKYCHENEY]

First tell tale sign that your approaching "full" is the smell. At 3/4 tank, my tanks start to fumigate a little. Time to pump out at that point. My Hart Tank Tender usually reads about 3/4 then.

Ditto

 

[Angela]

Maynard, I’ll pull the cover off the red hockey puck thing and see if I can fix it without a lot of frustration, but I’m not going to go nuts on it. I don’t want this kind of tank monitor for a lot of the reasons Sky describes. That tube did, in fact, rot off of my other tank and it currently has no gauge or warning light. I’ve only overflowed that tank once and that was we when we were in Bimini where they have no pump out. So, we just used the other two heads, instead. I’ve never overflowed the tanks in the marina.

Not having working gauges, I tend to pump out before the tanks are full and I guess at it depending on whether guests were on board and what heads were being used. My dad was here a few weekends ago, and with his failing kidneys, he filled the tank to the point that the light came on. I’ve never filled that tank that fast before, but I suspected it was about ready to be pumped out.

The way I see it, this is a good excuse for moving the new holding tank gauges closer to the top of this list.