Marc,
My question would be are you using a metallic core wire? I do and I strip and solder it to the terminal inside the spark plug boot. I use an automotive style boot, not the kit supplied plastic one. If you use a resistance wire such as you'll get from an auto parts store the center core is a carbon or graphite impregnated thread that needs to make good contact with the terminal. You can't solder resistance wire but it does require a good electrical contact to allow your plug to fire properly. Striping and bending it carefully back over the terminal is the best option. Hope this answers your question.
Tom