The high voltage wires are glued into a hole. There is a spike at the base of the hole to make the contact. I have used a hollow drill I made to get the wires out but you can do it with a screwdriver. Remember these coils are all 30 years old now and they weren't that good to start with. I would replace them with something modern. I tend to use the TEK KP03 coils fitted to Kawasakis etc but you need to make a small bracket to fit them. Any coil with a 3 ohm primary will do!
On the 900 there are often faults in the tiny wires from the ignition trigger coils.