more than one light comes on at a time , bad earth usually when 2 earth wires or more on one earth bolt. bad earth wire feeds next earth wire

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this is what happens bad earth wires carry current creating following continuose Circuit Example
Consider a very simple circuit consisting of four light bulbs and one 6V battery. If a wire joins the battery to one bulb, to a second bulb, to a third bulb, then back to the battery, in one continuous loop, the bulbs are said to be in series. If the three light bulbs are connected in series, the same current flows through all of them, and the voltage drop is 1.5 V across each bulb and that may not be sufficient to make them glow. each light becomes dimmer and dimmer