Dancing temp' gauge

[Cloggy Saint]

Once my temp' gauge reaches normal running temperature it starts to jump and flicker all over the place. Giving the dash a good smack settles it down for a while but it always returns. I had this before and replaced the gauge in the cluster but it still did the same. The nut on the back is tight. Any ideas?

[Brianmoooore]

If you're sure it's not the nut, and is associated with the cluster, not in the engine bay, then take the gauge out of the cluster and give the tracks on the circuit board that are relevant a good inspection for cracks and defects, especially where the gauge connects and around the blue socket.

[Cloggy Saint]

I assume if the brown sensor was dodgy then smacking the dash would have no effect?

[Brianmoooore]

Depends how hard you smack the dash! Brown sensor doesn't fail very often, unlike the much higher resistance blue one.
The plug and socket under the inlet manifold, where the injector loom joins the main engine loom (facelift only) is a likely trouble spot though.