Headlight cannot be switched off

I am driving a 17 year old Proton Wira, and the light switch suddently became faulty: I cannot switch the head light off. When I turned the light switch to off position, the Instrument panel light went off, but the head light remain lighted. I pulled off 2 light fuses from the engine compartment, but the head light remain on. Eventually I had to disconnect the negative terminal of the battery. An hour later, I tried a couple of times to reconnect back the battery and the light came on, i.E. The problem persist. However, the next morning, I reconnect back the battery, the problem disappeared by itself, i.E. The head light were off. What could have be the problem?