How do you check a fuel tank Guage on 3950 Toy Hauler?

I have an 09 Cyclone 3950 with generator. The fuel tank guage has worked fine for ongoing four years. Just before leaving to come down here to Tucson I checked the guage and it showed about a quarter tank. I filled it thinking I would put in 15 or so gallons but it only took about five. The trailer was level. The guage level to the best I can remember didn't change. (short memory)

Getting down here to Tucson it reads empty. I pulled the cover off and checked to see if there is any power to the guage. It reads differently between the terminals but I don't have a clue what the voltage difference means.

Anyone know how guages work, what I should check, etc. etc.:angel:

I have never checked mine, but - many gauges use some type of float in the tank with a variable resistor.
Your gauge could have 12 volts on one side and then through the float to ground on the other.

So if you have 12 volts on one side of the gauge try using a test light between the other terminal and ground. The bulb will act somewhat like a resistor. You could use a jumper to quickly ground the one side of the gauge to see if it moves.

B+ on one side - other side open - gauge should read empty (or full)
Ground the other side and gauge should read the opposite of ungrounded.

The lead coming form the tank at the panel should show resistance between the lead and ground, and that should change depending on the level.

Hook up a gauge and pump fuel out into a 5 gallon gas can, see if it changes.


Take a look at this page
http://auto.howstuffworks.com/fuel-gauge1.htm

http://auto.howstuffworks.com/fuel-gauge.htm

There are several pages to this link.

Do you have 12 volts on one side of the gauge?

Do you have some resistance between the tank sending unit and ground?
if not first place I would start looking is at the tank sending unit see if the wire is loose or broken off.