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Friday, October 23, 2009

Probing the Problem

My rig is an older 1975 Fleetwood motorhome and my problem is in how the wires are routed for the fresh water tank probes. The monitor panel does not read accurately for the water tank. The probe is in an upper corner of the tank and is vertical, top to bottom. There are two disconnected wires on the terminal protruding from the top of the probe. Any suggestions?
Jim, (Nuevo, CA
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Jim, considered “state of the art” in 1975, that vertical probe consists of a square plastic center core outfitted with five, metallic rods positioned on the outside of the plastic core. The rods extend vertically into the fresh water container to the individual depths as depicted on the monitor panel. The fifth probe is considered the “common” probe and will be the longest metal rod on the probe assembly and it’s usually located on one corner of the square center core. All five of the metal rods were prone to develop mineral deposits after years submerged in the fresh water. 

The probe assembly can be removed for cleaning by disconnecting the five wires (or three in your case) and unscrewing the complete assembly from the fitting on top of the water tank; it’s a simple pipe thread. Clean the rods with a soft bristle brush and perhaps some light steel wool. Be sure to thoroughly rinse it with fresh water before re-inserting it into the tank. 

The routing of the harness throughout the RV can be confusing. It’s quite possible the four individual level wires are run in parallel with the same levels on the two holding tanks and are routed to the respective holding tank locations before they terminate at the monitor panel itself. Each of the three tanks has a dedicated common probe and all three are eventually routed to the monitor panel location. It is nigh impossible to determine exactly how the harness is actually routed inside the RV. It may be possible to run a new five-wire harness from the top of the fresh water tank directly to the monitor panel, or it may be necessary to run the new harness to one of the holding tanks. Each level on each tank will share the same colored wire; in other words, the wire at the 1/4 mark on the water tank will be the same color as the wire at the 1/4 level on the two holding tanks as well. Simply match up the colors and your monitor panel should indicate the correct level in the fresh water tank. Use wire nuts to connect the wires from the new harness to the probe assembly so you can remove it for cleaning in the future. 

If the water tank still does not register on the monitor panel or the two cut wires are too short to splice onto, I would consider upgrading to one of the newer designs of monitoring level indicators; one that is non-evasive and easily installs onto the outside of the containers.

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