Temperature gauge in GQ sometimes works

[Majestic]

Hi everyone, I was wondering if you could help me out. I have a TD42 GQ Patrol and it's temp gauge works on and off. During a drive it won't work then it will then it won't as if it has a mind of it's own. I think it could be a loose earth somewhere but I am not entirely sure. I was wondering if anyone here has had that issue and what it cause was and how it was fixed?

Going away camping in a just over a week and I wanted to see if I could get it fixed before I go.