Ignition Switch problem

Hi I have a 1989 Honda Civic Dx hatchback and I have a question about the ignition switch. My engine shuts off as soon as I let go of the key, unless I get it in a certain spot and it will stay on. I've checked the switch and the contacts on the black piece of the switch, the one with the wires soldered on to it have melted.

Is it possible to buy this part, and how would i go about installing it?
Any help would me appreciated.
Thanks in Advance