temp gauge on a 90 defender

hey all ive got a 90 e reg fitted with a 300tdi and when the ignition power is on the temp gauge reads half hence when it heats up it gose over the red the gage is earthed and the other wire runs to the temp sensor that has one connection the wire from the gage is this correct or is it the rong sender? or a bad earth ?

What engine you have before
I think you need a new sender mine does the same

no idea only bought it the other day the fuel gage dosent work due to not being connected so will do that next weekend and ill try a new temp sensor thanks

Not a sensor a sender
The gauge ain't a match I don't think