Hi,

recently had a lot of welding carried out on my 1.9D van & upon collecting it I noticed that the temp. gauge was fickering. After a short drive the gauge stopped working & since then I tried various things to get it working. The gauge's needle it now pointing down. I've cleaned the electrical contacts & temporarily disconnected the main negative battery lead, as a member had suggested, but nothing has changed.

Can I please ask for your kind assistance to rectify this problem?

I had similar problem some years ago when gauge kept reading in red, fiat at Portsmouth assured me engine was NOT overheating. Auto electrician at Haydock sorted it when he soldered (resoldered) the earth strap clip located at the back of the battery, I thought it merely held the negative cable out of harms way, but infact the insulation is cut away and the clip contacts the inner cable.
I'm now experiencing similar problem on my 2.8TD so did similar to the negative cable below battery tray but unfortunately not sorted problem, next step is to replace temperature sender plug, unless someone knows better solution!!:

Remove the cover over the instrument cluster and disconnect the wiring to the temp gauge. Leave it for a while and then reconnect (it is a plug and socket) it will probably work. It is believed to be caused by a build up of static. Disconnecting drains away the static. If this makes no difference, you need a new sender.

Check your main earth lead under the bonnet. Its condition might have a part to play in this. They are known to be a poor design and quality.