Hi, I got a peugeot 407 1.6 hdi diesel 2006. Its fuel gauge is not working as the empty fuel tank warning lamp in always on and the needle is at rest where shows empty fuel tank, I checked the fuel unit sender read 273 ohms and after adding £30 ( about 21 litre) diesel it read 165 ohms which made me think the unit sender itself is working. I disconnected the socket which is connected to the fuel unit sender, this socket has only two wires white and green and after turning on ignition, there is positive charge in both wires even when they are not connected to the unit sender. The white wire reads 5.22 volts and green one 5.13 volts, and seems non of them is ground wire ! Wanted to know if one of them should be positive and one negative? Does the car have wiring problem? I checked both this wires until fuse box and they were no melting sign and they both receive this voltage from fuse box. I opened the dashboard speedo and checked the electric kit inside, there where no sign of melting and fuel gauge needle moved with finger which made me sure its not stuck and is not freezed. The computer displays fuel cap sensor faulty and I checked it reads with fuel cap on 150 kilo ohms and with no fuel cap on about 15 ohms and the fuel cap magnests are both in place.