Hi dave, I had exactly the same problem and its due to the connector melting on the back of the bulb this shorts the fuse and melts the positive terminal on the fuse box...
I drilled out the positive and kept a spade connector to the negative and then ran a new fuse from the original (+) wire to the headlight connector.
Then changed both headlight connectors to the ceramic type at most all this will cost £10.
Hope this helps
Tom.
