Ok. so I checked the earths and also moved one of the earths to body to a better place and added another on for the head.

This seemed to clear up the issue of it going up and down quickly. However, it will still be all over the place. I had the gauge shoot up to red after 2 miles of driving, pulled over incase it was over heating only to find that the fan's hadn't even come on yet. Switched of the car, started it up again and the temp gauge jumped straight down to the middle!?!

I bought a new sender but the issue persists.