Driver door, no interior light, but key warning sounds? 1979 W123

I keep meaning to ask y'all this one too...
So my driver-side door opens, and the interior light doesn't come on. But the passenger-side one does. One night, I figure what the heck,
I'll just swap switches and get a new one for the passenger side "one day."
Pulled the driver-side switch, and it tested ok. Somewhat boggled and having started the job too late at night, I put it back together and didn't worry about it. Then I noticed, if I leave the key in the ignition after driving somewhere, and open the door, I get a buzzer 'til the key comes out.
So, it appears that part of the switch's function works, but part doesn't. Does anyone have any ideas what I'd look at for this one?
thanks, -tom!
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The driver's door switch to the overhead light is wired through the seat belt / key-in-ignition / headlights-on warning buzzer. When you learn what that device costs you'll know why it was not replaced.
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2007 T.G.Lambach. Publication in any form requires prior written
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T.G. Lambach wrote:

So all of those other functions could work fine, and just the overhead light function be busted? I'll have to poke around for one of those then, or maybe hotwire it all somehow since the passenger door activates the overhead light just fine.
thx, -tom!
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