temperature gauge help

I have converted a 2.5 na to a 300tdi but need bit of help with wiring the temperature sensor up. At the dash end I have a black wire with a ring on witch is the earth and then I have a all green wire that connects to all other dash clocks ect I have a blue and green wire that gose from the dash to the sensor I believe. But when I trace the wire its ends up been pluged it tto a multi plug and the gose to the low current feed to the alternator so I cant plug the sensor in. Is they some think I have wired up worng any help or tips would be great as iam at a dead end now. I no that the temp gauge wont work as it should