The sending unit for a Ford Ranger is actually built with the fuel pump. You can purchase this part as a whole. The sending unit itself is responsible for operating your fuel gauge. When the float is down it sends a signal to the fuel gauge that your tank is low on gas. The float will rise with the gasoline in the tank. That is why it is called a float. The whole assembly is complex; replacing the whole unit is the easy way to go. Replacing the fuel pump may not be a bad idea anyway as running the vehicle or trying to start a vehicle with a dry fuel tank can actually damage the pump.
Jack the back of the truck up. Be sure to chock the front wheels.
Empty the contents of the gas tank. This task will be easier as the tank is easier to manage without the extra weight. The gas tank will have a plug on the bottom of it.
Locate and remove the straps holding the fuel tank, There should be two straps holding it up. You will remove four bolts.
Lower the tank to the ground. Be careful as there are wires running to the tank.
Remove the fuel line hoses. They should unsnap from the top of the tank.
Detach the wires from the top of the fuel tank. They are on quick release connectors.
Remove the gas inlet hose. This will require loosening a hose clamp. The hose will be on the back of the tank.
Unscrew the assembly on top of the fuel tank. You might need a hammer and a pry bar to help unscrew the top. The threaded portion will come off, leaving the pump assembly sitting in the tank.
Pull the assembly out of the tank. The sending unit and the fuel pump are connected together to an assembly. You will want to replace the whole assembly.
Remove the old O-ring on top of the fuel tank housing. The fuel pump/sending unit assembly will come with new o-rings.
Place the new O-ring where the old one came off. This will make a seal when you go to fill the tank up.
Put the top of the fuel pump assembly with the threaded top and place it in the tank. Be sure to tighten the top down. You might need the hammer and screwdriver to help get it tight.
Attach the wires to the top of the fuel tank. They should snap into place.
Slide the fuel line hose back on to the fitting. The line should snap on.
Using a jack or the help of a partner, lift the tank to the frame. A jack or a partner holding it in place will make it easier to put the bands back on.
Install the fuel inlet hose. Tighten the hose clamp snug.
Tighten the bands back to the frame. Tighten the bands snug.
Lower the vehicle from the jack. Put your gas back in the fuel tank. You can now crank up the vehicle. The truck may not start right away so you will want to give the fuel pump time to pump fuel back in the line.
When the tank is dropped and empty you can clean the tank out. Flush out any sediments by using water or gasoline. If you use water be sure to make sure the tank is completely dry before you attempt to put gasoline in it.
Be careful as this vehicle will be on a jack. Use extreme caution when working on elevated vehicles.