Fiat uno 45 H reg (91) electrical problem

I have an intermitent electrical problem with my Fiat. The temperature gauge leaps about if I brake, use indicators, turn on lights etc. This only happens in very hot weather or after I've topped up the rad. It stops
after a hundred or so miles (or until the water has boiled back off again). My garage said it was a problem with a low battery causing the alternator to spike and they've fixed it by replacing the battery but it's doing it again and has done this since I got it (2 years ago) and surely the battery would boil if this was happening. Help, any ideas would be great as my otherwise fantastic car is a nightmare to use when the dial leaps about, it's distracting if nothing else. Thank you
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I suspect you have a "high resistance" earthing problem - poor connection.
According to "Haynes" the earth connection for your fuel gauge is daisy-chained via the steering column switch unit to an earthing block which is located "dashboard - left hand side".
If I was you, I'd find that connector block and clean the contacts there.
I have no experience of the UNO - but would guess it to be a similar arrangement to the Panda, which commonly has earthing problems with a block causing all kinds of interesting/boring effects. That block has push fit connectors which have an integral small tab, which needs to be squeezed when you pull the connector off.
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