Tank sensor question (technical)

[dsherman26]

I was a little surprised while getting under the trailer to address a water filling issue. I was aware that there were sensors in the tanks that sense the water conductivity to detect the levels, but I assumed there was a wire for each probe. Looking at the wiring, I was surprised that the upper 3 sensors are all wired together to one wire, and the bottom one appears to be wired to ground. Is that correct? Looks like it's trying to measure the combined resistance of all the probes as each probe touches water; I was under the impression it just sensed that if any one of the probes has any conductivity, then the water was at that level.

[Mr. Dan]

They should all be wired separately... colored coded wires. See this thread ==> https://www.forestriverforums.com/fo...le-255236.html.

[dsherman26]

Interesting. That would make much more sense using one for each probe. I might have to go find the manuals for the panel in mine and see how it's supposed to be wired. It must be doing some kind of determination based on the total resistance since it does go through 2/3 and 1/3.

[Mr. Dan]

Can you post a picture?

[dsherman26]

There's not much to see. The wires from the tank go to the red terminal block. The red wire from that block goes to the blue wire from the wiring harness. The two white wires from the harness go to the white wire at the bottom of the tank.

[Steve-W]

The “red terminal block” is not a splice point but it is a resistor block.
The red wire to is what goes to the level display, the white is ground.
The resistance between the sensor wires is as follows.
RED TO ORANGE – 0 OHMS
RED TO GREEN – 68K OHMS
RED TO YELLOW – 188K OHMS

The level display displays the level based on resistance the circuit is completed when the water level in the tank bridges between the common contact (bottom) and the other three.

[dsherman26]

Originally Posted by Steve-W

The “red terminal block” is not a splice point but it is a resistor block.
The red wire to is what goes to the level display, the white is ground.
The resistance between the sensor wires is as follows.
RED TO ORANGE – 0 OHMS
RED TO GREEN – 68K OHMS
RED TO YELLOW – 188K OHMS

The level display displays the level based on resistance the circuit is completed when the water level in the tank bridges between the common contact (bottom) and the other three.

A ha! That makes much more sense. Still somewhat dependent on the water conductivity being in a certain range, but I didn’t realize that was a resistor block. Thank you!