I was waking up the neighborhood with the buzzer that would come on when I got out of my '81 Corolla with the engine running to open the garage door. There is a little box labeled buzzer underneath the dash. I found the buzzer by sticking my head where my feet would normally go (contortionist position), then sticking the key in the ignition and following the sound. I pulled out the plug going into box and now I don't get key in ignition with door open warnings, but neither do I get seatbelt warnings (I could probably do something more sophisticated with cutting select wires to resolve this I guess, but my belt is always on). On the other hand, doing something like this on your more spohisticated car would probably cause the check engine light to come on. The next level of fix would be to install padding around the chime.
Mind you, my conscience will be bothering me for the rest of the day

because anybody who doesn't wear a belt deserves at least the purgatory of 30 seconds of chimes. (I don't care if you're killed outright, but maintaining the brain dead and severely maimed ups insurance premiums for the rest of us)
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1981 Corolla Wagon, 5-speed, 159k miles-- my winter wheels
1981 Corolla Wagon, AT, 125k miles-- my summer wheels
** I replaced a horn. Isn't that mod. enough?

**