Checking earths / maintenance on them is a good idea, but may not solve all your problems. Whats up with the windows, C/L and wipers ? Intermitt operation or not working at all ?
If the windows are working but becoming lazy & slow then probably due to the grease drying out in the hideous spiral contraption that works the glass up n down. I'm suffering the same - need to remove assembly, clean and regrease.
C/L - JohnC is best one to answer this but there are motors, solenoids etc. that are all linked and can give problems. Again, mine locks and unlocks from the fob but the internal electronic release on pass'ger side is not working 100% of the time (and no JohnC I still havent sorted it out yet

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Wipers, must admit, apart from the one wiper coming loose once, I havent experienced any problems. But search through the site and you may find some past posts that help you out depending on the symptoms.