The top fuse is for the horn and the interior light which work without the ignition being on.
The bottom one is for the indicators, windscreen wipers, heater fan, fuel gauge, brake lights and other items which only work when the ignition is switched on.
Neither fuse covers anything which could stop the running of the engine (basically the ignition system or the petrol pump) because it isn't considered safe to run these circuits through a fuse and have the possibility of a breakdown.
It is quite common for neglected cars to suffer faults related to dirty fuseboxes. A few minutes cleaning yours up will be time well spent but it shouldn't make any difference to the running of the car - unless yours has been modified in some way. These cars, over so many years, do seem to suffer from "improvements" made by previous owners
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