Here's a good description explaining how to test the leads, if you find one that doesn't give any reading then that's a bad one. https://www.ngk.de/e...gnition-cables/
The plugs and leads I normally change Every 3 years (or sooner if your doing a high mileage) and the coil could last the life of the car or it can break down at any point ( it went on my fiesta at 35,000 miles and was replaced with an OEM one which was still ok when we sold the car with 101,5000 miles on it in March) it's just the luck of the draw.
When I change ours I'll be buying bosche super4 plugs as I used them on our fiesta and had no problems, throttle felt sharper as well.
I'm currently awaiting a new multimeter as my old one got broken and is no use so when it arrives I will use that guide to test the leads and see where I am from there. I will keep this updated as it may help others.
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