Question regarding water tank gauge wiring

Discussion in 'General RVing' started by PSmith, Jul 20, 2009.

  1. PSmith

    PSmith New Member

    Hi all. Long story short I am rewiring a friends toy hauler following an incident with an angry dog getting into his side yard and chewing up all the electrical on the bottom side of the trailer.

    I've rewired everything so far with the exception of the clean/grey/black water tank sending units and I need some insight.

    A generic image which I found online of the tank gauge set up that is on the trailer is pictured below.

    On the bottom side of the trailer, each of the tanks has four studs sticking out of the side for the sending unit wiring, twelve studs total between the three tanks. The studs are arranged in two banks so to speak, one stud on the bottom left of each tank and three studs stacked vertically on the right bank, each about 4"s higher than the one below it.

    I found four wires coming through the floor which I am assuming are the wires back to the gauges but unfortunately cannot confirm this without a major overhaul to the cabinets and interior of the trailer.

    From what I have read, sending units of this style rely on the fluid in the tanks to conduct electricity. If my understanding is correct is it safe to assume that each of the lower left studs could be a ground wire and each of the other three studs per tank would be fed by one of my other remaining three mystery wires? One wire per tank, wired in parallel to the three right bank studs?

    Please excuse my ignorance and thanks in advance for any input. The plan is to head back out to the town my friends trailer is in this weekend to test the four wires I have to hopefully get the tank gauges back in working order.


  2. TexasClodhopper

    TexasClodhopper Senior Member

    Re: Question regarding water tank gauge wiring

    Welcome to the forum, Patrick!

    Without being there and seeing what you are seeing, I would tend to agree with your assessment of the wires, (although I can't understand how there isn't enough wire remnant left for you to match with.)

    Use a voltmeter to determine if there is any lethal voltage on the wires in question.

    If there isn't, get your friend to watch the panel inside as you touch each of the other three wires individually to one of the wires that you pick as the 'ground' wire. Some light should light up in the panel.

    The lower light indicates a lower fluid level on the tank and the lower stud.

    Each tank should have its own set of wires.
  3. PSmith

    PSmith New Member

    RE: Question regarding water tank gauge wiring

    Haha, yeah. I couldn't believe the bottom of the trailer myself. This dog mush have had one hell of a digestive tract; 95% of the wiring that should have been under the thing was no where to be found.

    Thanks for the suggestion, that was the plan for this weekend.

    I have four partially chewed up 14 gauge wires coming through the floor directly below the cabinets the gauge display is mounted in. One brown, one green, one red, one white. On each of the tanks I have four 22ish gauge wires exactly as pictured above, one brown, one green, one yellow, one white.

    I've rolled around under the trailer trying to find more possible locations where wires could have been routed to no avail.

    Any further insight regarding the busing of a single wire down the three studs of each tank would be appreciated.

    Thanks again.
  4. TexasClodhopper

    TexasClodhopper Senior Member

    Re: Question regarding water tank gauge wiring

    More clues to the wires will be found on the back of the gauge display, also.

    Start with: white = common, green = 100%, yellow = 50%, brown = 25%

    I think the 14 gauge wires are not part of the 22 gauge wiring directly. That is probably confusing you, but look at the back of the gauge display.
  5. LEN

    LEN Senior Member

    Re: Question regarding water tank gauge wiring

    Think I would look at a reroute of the wires from the panel. With the dog chewing and pulling there's most likely more problem than just the wire that is missing. And Tex is right on starting at the panel to see what goes where and the colors involved.

  6. PSmith

    PSmith New Member

    Re: Question regarding water tank gauge wiring

    The back side of the panel wires that I can trace through the circuit board don't correspond (color/gauge wise) with either the four 14gauge wires under the trailer or the wires at the tank senders. Unfortunately, and without some major carpentry work, I cant determine where the wires from the gauge display go once they disappear into the cabinetry. The fact that there appeared to only be one wire for each of the three LED sets at the gauge panel lead me to believe the the 14 gauge wires on the bottom side were related some how. I think I'll make myself a 20ish foot long jumper wire to see if I can get any continuity between the 14 gaugers and the panel first thing Saturday morning.

    Thanks for all the help so far, I'll keep yall posted.
  7. PSmith

    PSmith New Member

    Re: Question regarding water tank gauge wiring

    Oh, and also, would anyone happen to know who the original manufacturer of the gauge display I posted up above is? The one pictured has the Lazy Daze logo on it and the exact same unit I have is on a Weekend Warrior. If I could get a legitimate wiring diagram from the supplier my problem would be solved.
  8. PSmith

    PSmith New Member

    Re: Question regarding water tank gauge wiring

    I was able to free up some time today to take a look at the trailer.

    The four 14 gauge wires coming through the floor were for the gauges, they are as follows:

    Green wire - fresh water gauge (12v)
    Blue wire - grey water gauge (12v)
    Brown wire - black water gauge (12v)
    White wire - ground.

    If I was to jump either of the above wires to ground I would get a 'full' tank reading, therefore zero resistance across the sending units equals full.

    Now, on to my question.

    Can anyone break down the wiring in this image and relate it to the four wires I have under the trailer to hook up to the sending units?


    I hooked the wires to the tanks up so that the 12v wire that corresponded to each tank was bussed across the right bank of studs (green/yellow/blue) and hooked up the white ground wire to the stud on the left.

    I understand from what I have read that these sending units are far from accurate and are prone to display false readings, that being said, both of my waste water tanks are reading full (they are empty or 1/4 full at most). The clean water tank reads full also, though I have no idea how much water is in it.

    Any more ideas? Am I wired correctly?

    Thanks a lot guys.
  9. TexasClodhopper

    TexasClodhopper Senior Member

    Re: Question regarding water tank gauge wiring

    Patrick, if I might hazard an educated guess (also know as a BWG [Big Wild Guess] ).

    Assume the studs are the 3 connections of a potentiometer style level gauge. Either the top or the bottom would be positive and vice versa. The middle would be the wiper or level take off.

    If that is a correct assumption, then you will have 12 volts on either the top or bottom stud and ground on the other one. The middle one will vary with the level of the fluid.

    If that is all correct, then the middle wire is the one that goes to one of the four 14 gauge wires that go to your gauge readout.

    Boy! That's a 'hole lot o' assumin' goin' on aroun' heah! :clown:
  10. Quick26

    Quick26 Junior Member

    I have dog that did same thing on my 2005 FS3400

    I know it has been a few years, but you are missing an important part. My dog ate all the colored wiring and fresh water overflow tube on my 2005 FS3400? This happened 6 months ago, and I finally had time to investigate. I went to local dealer who let me look under a WW trailer to check wiring. I took some pictures. The main thing you and I are missing is what is called a Holding Tank Sensor. I have attached some pics. This part is basically a resistor network. These colors don't match your on-line pic, but match the WW trailer I looked at. I may have some insulation remaining in my islets to check on sensors to see if colors match. Salesman said these do come in different resistances, but for $12 each I will try these first. I will post back in a few weeks if I have success.

    Attached Files:

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