Can you guess the cause of this fault?

[marlbstag]

Had a very strange electrical fault on the way home today, stuck in traffic due to long term roadworks the temp gauge suddenly went to 3/4 mark and volt gauge dropped to 12 volts, engine was running ok, not getting hot. All the way home and later in evening on run to band the same, temp gauge at 3/4 volts 12v but on way home having to use headlamps volts at 9v and temp gauge in red !! Again engine not overheating, but headlamps annd dash lamps dim but ( this gives a clue) hittng a bump in the road the lights would brighten and dim. Can you guess the fault?
Yes i did find it luckily because it was dark !! Martin.

[milothedog]

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Loose battery lead!

[Greenstag]

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Something earthing out and causing a spark..which you could see in the dark?

[marlbstag]

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Spot on !! the earth lead from battery to body was just loose enought to make and break and in the dark i could see glow from the arc it was making!! That will teach me to wipe around the engine bay just before the National which I had done that lunch break. Still strange how the temp gauge went upwards as the volts went down? Martin.