Bavaria 30 gauge [water, not fuel]

[Bavnav]

Hi.
My fuel gauge appears to be stuck at 1/4 tank. Since I bought it last August (2006 model) the gauge has not moved from 1/4, when switched; when unswitched it returns to empty. I am quite sure I am pressing the correct switch, the bottom one below the batteries symbol. I also note that there seems to be posts about bigger boats with a similar problem showing a constantly full tank. I have put 40 litres in recently (where it says diesel) however, there is no increase in reading.
Does anyone have any advice?
Regards,
Bavnav.

[Subject amended by Nigel]

[Trapeze Artist]

The gauge you are looking at is water level. Try the fuel gauge that is on the switch panel just below the steering wheel. 

[Bavnav]

Hi.
Many thanks for the info. You have solved a myriad of problems and the way looks clear.
Fair winds,
Keith

[Trapeze Artist]

Although I've not done a comprehensive test, I get the feeling the water gauge only displays 1/4, 1/2, 3/4 and full. So it's effectively a low-resolution digital system masquerading as an analogue display.

At least, I never seem to see the gauge in any position but those, and a small top-up or water useage seems to have either no effect or a 1/4 tank jump.

[Bavnav]

Hi.
Yes, that is interesting. I will remember that when I fill the tanks next month.
Many thanks,
Bavnav

[Nigel]

Although I've not done a comprehensive test, I get the feeling the water gauge only displays 1/4, 1/2, 3/4 and full. So it's effectively a low-resolution digital system masquerading as an analogue display...

It is indeed, the sensors cause a resistive ladder to be switched in, so if one of the sensor rods doesn't send a signal, the reading goes nonsensical. I've removed the gauge and fitted four LEDs.

[Moodymike]

Could you describe the LED set up?

[Nigel]

Could you describe the LED set up?

Sorry for the delay, I made a note to reply then couldn't find the thread: I was looking for a thread about the water tank gauge! I've amended the subject for future reference.

My B47 has a PCB behind the (Panel 20) switch panel; this PCB is marked PB-42. The water tank sensors on my boat are rods of different length which conduct via a longer common rod if the water level is touching them when the gauge switch is operated. 

The PB-42 schematic is attached (spelling as original German) as well as my composite image showing the PCB with the component details. Marked in red on this are my ¼ ½ ¾ Full take-off points corresponding to the collectors of the 4 transistors. These are pulled low when the corresponding rod is immersed. I fed these to 4 LEDs, with 4 dropper resistors wired to the common switched positive marked SW OP