Distributor cap & HT leads

Hi everyone, I've got a 1983 mk1 gti tin top. I was driving the other day and it started misfiring I pulled over and an ignition lead had come off i replaced it and carried on. Once I got home I took a closer look and the point's inside the cap have melted and melted the leads as well. Very frustrating as they were only on 3 months and were quite expensive. Does anyone know why this would happen and how to fix it? I definitely need a new distributor cap are there any particular makes that are better than other? 
Thanks I'm advance

It's a Bosch distributor cap I've just spoken to the manufacturer of the leads and they tell me it's the wrong distributor cap that it needs to have pins only it just has female connections. I'm at a loss at the minute 

Two types of cap, one has pins, one doesn't. Leads must match the cap. If it is an 83 then it shouldn't have pins.

Thank you so much that explains a lot 👍