hjfrans: it's much easier to remove the bed from the truck than to drop the tank. Plus you don't have to worry about spilling fuel or the tank being too heavy with fuel in it. It's also easier to get to the fuel connections to the pump and the plug is right there as well. If you tear up the lock ring for the float/sender unit, trying to get it removed, you can get a new one from your local Ford dealer for only a couple of bucks. I think they come in a couple of different sizes, so just let them know the diameter you need. To test the sending unit once it's out, you'll need an analog voltage/ohmmeter tester, one with a needle that shows the reading. You might be able to use a digital meter as well but usually the analog type shows the change better. The sending unit will probably be a plastic box with slots in it which is attached to a metal tube for fuel return. The float arm will come out of one side of the box and the other side of the box will have the pivot end of the float arm go thru a metal support for the box attached to the tube. This support end is the ground for the sender and the wire is the positive end for the gauge. Connect one wire of the meter to the wire from the sender or to the pin it goes to on the plug and the other meter wire to the tube. You'll be doing a resistance check so set the meter to ohms. There may be more than one scale for ohms but you should see a change in the needle on most of the scale settings. With the meter on and the float rotated down to what would be the low point in the tank you should see a reading on the meter. Then slowly move the float arm up to see if it makes the needle change to indicate some higher or different numbers. You should be able to see the needle move in a steady pattern to indicate the change you are making in the position of the float arm from top to bottom. And it should show any dead spots as you go. It's usually the sending unit that goes bad. If the gauge goes bad they usually don't indicate anything. When you put the sender back in the tank, try to make sure the fuel filler hose won't affect the float arm travel which might give a low reading when you know it's actually full.