Just recently picked up a 1985 740T 4-speed manual with overdrive sedan with 217k. Synthetic oil has been used for at least the last 80 thousand miles, and the prior owner claims to have had no particular turbo issues, nor much in the way of problems with the car in the seven years he's owned it.

So I drive it home. And I go out later that night to take it for a spin after I've put insurance on it. And I put the key in. _And the beeping began_. (Also, I noticed the interior lights seemed to have stopped working.) Whenever the key-insertion switch on the ignition is tripped, the car beeps, even if it's off.

Somewhere in the seatbelt alarm or door-open alarm, something has gone terribly, terribly wrong. The beeping really starts to get to me after about ten or fifteen minutes.

What's the easiest way to disable this noisemaker?

And also, any particular considerations for this vehicle? Things I should worry about, or ask a mechanic to check out?