It's probably what Kirk said...., the door switch shorting out
*edit*
I was just txting the new owner of my car and i remembered something....,
i had disconnected the door buzzer on my car, try this.....,
under the fuse box there is a long-ish connector, i'm not sure what all the wires are for, but i'm pretty sure for this part you can just pull the whole thing out...., now chuck a fuse in, if it holds then it's your door switch i reckon
somehow i worked out which wire was for the door switch without using a wiring diagram or a multimeter, but with no car, i can't tell you which one
