Courtesy lights stay on all the time

https://www.corvetteforum.com/forums/c6-corvette-general-discussion/1700828-help-rearview-mirror-lights-won-t-turn-off.html
This forum from corvette may shed some light on what to do.

do you have the light switch on? also there is a little switch on the door that gets pressed when you close it this part could be broken causing the car to think the door has been left open thus leaving on the courtesy lights

This is both a courtesy and safety issue on many high end vehicles. The light from the interior lights can cast enough light to get to front door and possibly show dangers in your path. And after first getting into you car and starting it, you can check the back seat for any unwanted hitchhikers. As for the 10 minute timer, I don't know if this can be adjusted. A Chiltons/Haynes repair manual for you car may have that answer, or, the Buick dealership shop foreman. Best of luck.

Underneath the dash on drivers side,

There are little switches in the door jams that depress when you shut the door. One of these is broken or disconnected....no other real possibility here.

Fig. Headlamps (1999) - ZOOM LINK

Check links...

Fig. Courtesy Lamps, Page 01 (1999)

Fig. Courtesy Lamps, Page 02 (1999, Coupe, Convertible/Hard Top)

Fig. Courtesy Lamps, Page 03 (1999, Convertible/Soft Top)

Fig. Courtesy Lamps, Page 04 (1999)

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Hi Dennis,

Your courtesy lights are controlled by your Body Control Module (BCM). Normal operation is for the courtesy lights to stay on for 2-3 minutes after the door is closed, then turn off.If they stay on longer than about 3 minutes, then there are several possible causes:

1. You may have the "courtesy lamp override switch" in the overide position in the dimmer control on the dash.

2. you may have a door that is not completely closed. You need to check ALL of them.

3. You could have a defective door switch or dimmer control switch

4. you could have a short to ground in one of the door control switch circuits, causing the BCM to "think" that there is a door open.

The CORRECT way to fix this would be to scan your BCM for fault codes and also read the BCM data to find out if it is showing one of the doors as being open when they clearly are not, so you will know which door is causing the problem.

Removing the courtesy lamp fuse will NOT completely fix the battery drain problem if these circuits are shorted or malfunctioning because the BCM will STILL be "trying" to turn these lights on and this will also cause an excessive draw on your battery. However, removing the 15 Amp fuse marked "CTSY LMP/MIRROR" located in the instrument panel fuse block will get the lights turned off and at least slow down how fast your battery is draining.

check button switch at door

Have you check the door ajar switch in each door?

There is a module called the delayed entry module, it keeps the courtesy lights on for about 30-40 seconds when the door is opened, by what you say that may not be the problem, without the load of the light bulbs the timer will not work in the module, this throws off many techs. Have you had the battery tested?? even if it is new it can have a problem, I put three new batteries from Kragen in my Corvette in 1 year, I also thought the system had a drain, but it was the battery every time, finally bought a Delco battery and never had an issue again.