Classic/Antique Car Repair: Auto electric short circuit, daihatsu mira, plastic casing

Question
QUESTION: My question is concerning a possibility of a short circuit in the auto electrical system and is quite general in nature. The ignition key gets slightly more than warm when in use. I have replaced the barrel which incidentally is a plastic casing. It is connected to the car wiring harness via a 5-terminal female socket. The insulation of the wires and the socket have melted to an extent but still seems usable. This is the second barrel I have replaced. I am thinking of replacing the socket just in case it helps to reduce any resistance. How do I check for any possible shorting in the circuit.

ANSWER: I have several questions. What is the year make and model of the car? Next, what accessories do you have in the car such as A/C, sound system with an amp, or any other accessory that is switched through the ignition switch? High current draw through the ignition switch will cause the heat as well as a defect in the switch or the connector causing resistance. Please let me know and then we can figure out a cure.

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QUESTION: The car is actually a 2005 Daihatsu MIRA 660 cc derivative in Malaysian guise.
Accessories include an air-conditioner and radio/CD player only.
The problem occured only about 6 months ago.

Answer
I don't think that I have even seen one of those much less worked on one. However that said I think that I would start checked amperage loads on the system. Do you have a digital multi meter and if so what brand and model? It is possible that the A/C compressor clutch or the blower motor may be developing an internal short that is increasing the amperage draw and placing a load on the ignition switch, so let me know about what kind of meter that you are using and we will go from there.