Switch needed

That is the key in warning buzzer switch. I found a new one on eBay for mine. The question is what caused it to melt down? The buzzer is in the horn relay and is supplied 12 volts looking for a ground thru the switch to the driver door switch on my 71 Demon. I also replaced the molex connector on the ignition switch with a weather pack connector due to the new wiring harness in the car and the new ignition switch making poor connection with the new parts.
All the wiring is in bad shape so I am replacing all of it main harness headlight to taillights underhood etc. The new harness didnt come with it .