Waste water gauge

[Sessa Lel]

so you are about to order a new sender then!
following recommendations here, I bought and infrared Philippi sender, not cheap, but touch wood still works 10yrs on!
Non contact level measurement (UTV) | philippi elektrische systeme GmbH %

EDIT: Mind, it's not a straight swap to the two wire one you have!

cheers

V.

I ordered the sender, before I did extra checks with your help, so once gauge arrives, I will try, (knowing it will be the same, and hopefully send it back) but I'm now sure it's the sender. Will keep you informed.
My sender has 3 wires 12v, earth, and signal. Most of the senders have 2 wires, 12v and signal, so if I get a 2 wire sender, I will attach an earth to one of the fixing bolts (I have a plastic tank)

 

[vas]

I ordered the sender, before I did extra checks with your help, so once gauge arrives, I will try, (knowing it will be the same, and hopefully send it back) but I'm now sure it's the sender. Will keep you informed.
My sender has 3 wires 12v, earth, and signal. Most of the senders have 2 wires, 12v and signal, so if I get a 2 wire sender, I will attach an earth to one of the fixing bolts (I have a plastic tank)

re sender, you are giving 12V and earth before measuring output vs earth, right? a three wire sender unless it's powered wont show any output (pretty sure about that!)

 

[Sessa Lel]

re sender, you are giving 12V and earth before measuring output vs earth, right? a three wire sender unless it's powered wont show any output (pretty sure about that!)

I was checking resistance on the wires straight from sender, ( sender disconnected) I was getting no reading on Ohms tester.

 

[wonkywinch]

Minor point, on DC circuits, it's not "earth" as such but the zero volt or negative connection. If a fluid level sender only has two connections, then it's simply a variable resistor and won't need any earth/negative connection etc and is wired in series with what is effectively an ammeter (the gauge) that measures the current flow increasing or decreasing according to the position of the variable resistance in the sender.

The three wire senders work like a voltage ladder, +12v on one end of the variable resistor, 0v/neg on the other then the third (output wire) supplies a voltage proportional to the position of the sender, eg 0 to 12v and the gauge is a voltmeter (not ammeter) reading that voltage as anywhere between "full" and "empty".

 

[vas]

so test again, mostlikely sender is fine.
One silly Q: has the combination of sender and gauge worked before and just failed, or is it a new to you boat and you've never experienced the system working?

 

[Sessa Lel]

I bought the boat last November, the gauge was not working, part of the deal was that a new sender would be fitted as part of the sale, so I had a new sender fitted, and all was working.
Gauge stopped working about 2 months ago, in theory part should be under warranty, but as part was back order when we took delivery, sender was sent to me and I had it fitted.
So not sure where part came from.