RV Repair: Hi Lo trailer holding tanks., hi lo trailer, holding tanks

Question
We have a 2004 Hi Lo 27T trailer. The gray water tank sensor indicates full all the time . I can find only one wire going to a probe on the side of the tank .Can you tell me if that could be for the level sensor?

Answer
the level sensor is going to be a probe, most likely, but it will be high on the tank, on the side near the top or on the top.  It may be bad or may have something stuck on it.  Maybe a piece of food or a piece of paper towel made it down the sink and is stuck to the probe.  Pulling the probe out would probably knock it off.