Scirocco Register

as the tittle says really, i had the engine out to get a new gearbox in and when i put it all back together the temp gauge doesnt work, the red led blinks at me, but thats all, it fired up first time replaced every thing the same.
i dont know any thing about the electric side of the cooling system so any help would be fantastic

Check to see if the little connector is fitted. it is a single wire connected to a terminal near the plugs.
If it is give it a rub down with some emery cloth.