How to get to the fuel gauge sender unit on a Volvo 240.
Disconnect the battery negative lead making sure that you have the radio code if applicable. In the luggage compartment lift the carpet and you will see an inspection plate in the floor. Remove the plate to see the top of the sender unit. Disconnect the earth (ground) wire and the lead from the sender unit terminal. The sender unit is held in place by a locking ring which can be taken out with a special tool or by using a piece of hard plastic and a hammer. The plastic is to prevent sparks. Place it in one of the cut-outs in the ring and gently tap it until the ring comes loose. Lift the sender unit out of the tank. It is possible to make the tool if you want to.