PEUGEOT 306 spark problem

If that's exactly your coil, it's impossible for a spark plug not to fire unless the coil is faulty. This is because these types of coils work with waste sparks. The same coil sends a spark to two paired cylinders, meaning the pistons rise at the same time but on different strokes, either compression or exhaust. So, the spark jumps at both spark plugs simultaneously. If you don't believe it, check it. If your firing order is 1342, the outputs of cylinders 1 and 4 will fire at the same time. If you bring the two wires within an inch, you'll see the spark jump between them. You can do the same with cylinders 2 and 3. The spark can't jump to only one side if the coil is good. If it doesn't fire or the spark is very weak, the coil is faulty.

That's right, that coil pack is responsible for both cylinders. Try another coil pack and see what happens

Hi, what voltage does the cable that connects to the coil operate at? I've noticed it has two blue wires, one white wire, and one black wire

Hi friend, as the others have said, the problem is almost certainly with the coil. Try another one that you know is working. Regards.