Hello again Mike
I did a further test by connecting a jump wire directly onto the battery neg and the other end of the wire touched the pin in the plug which pushes onto the sensor, with the ignition switched on the gauge didn't move.
In answer to your question, no the gauge did not swing back and forth, it was stable when it was working, slowly moving as the engine got hotter.
You know Mike this is looking very much like you say, the gauge itself is shot.
I'll have to pull the instrument panel out, I'm not sure if I can test the gauge further once it's out as a final confirmation that it's a trash job.
I'll get back to you once it's out, taking instrument panels out of cars is a real pain especially when there is no workshop manual to cover it, I know in addition to the screws holding them there are a load of plastic clips which you have to try and spring out, they are normally an integral part of the plastic molding and more often than not break off.
When I took an instrument panel out in a different car, I ended up having to take the steering wheel off and of course the airbag, I remember I wanted to test something so had to reconnect the battery.
I switched the ignition on to check whatever it was and never thought any more about it, until everything was back together only to find the airbag warning light would not go out, so ended up having to take the car to a garage so they could use their laptop with appropriate software in order talk to the car and make it go out.
I was told that even with the airbag out of the car switching the ignition on trigger a fault, so i wont be making that mistake this time.
While I've got your attention I'd like to ask you about something else, the outside air temperature which is displayed on the in car display has started dancing up and down, I know it could be the outside sensor is there a way of testing them?
Thanks
Clive