Morris Minor Owners Club

Since fitting the correct speedo for the 1098 engine I have a slight problem. The fuel gauge is reading back to front i.e. when fuelled up it reads empty and as it is being used the gauge rises towards the full mark. So what do I need to do cheers

What colour is the gauge? And the age of the car ? Is there a voltage stabiliser on the back of the speedo - and is it wired to the gauge??