What's your problem?I have a 2003 Lexus RX 300, for some reason the open door warning light is on, even though all doors are closed. Its very annoying it keeps beeping while you're driving.

SOURCE: the open door warning light indicator does not go off .

There is a problem with the door switch the door is not pushing the switch in completely. Here is what you do close all the doors, then you open them one at a time with all the other still closed. start with the drivers door. open and look for the pin with that the door touches when you close its on the bottom close to the back of the driver's seat it has a black rubber covering it. Press with your thumb in and see if light goes out. Check all other doors in the same way you will see which door switch is not being pressed in completely when door closes. If you find it a quick fix is to pad the area on the door that makes contact with the switch to push it in, for example you can use one of those round sticky cushions that you use on the metal chair legs to prevent them from scratching your wood floor. However if you can solve the problem in this way you may have to take it to electrical mechanic or I will be able to provide more help. contact me and leave me a feedback. Good LUCK

SOURCE: 2003 Explorer door ajar light stay on when all doors are closed

The door switches sometimes stick. Spray some WD-40 or similar lube on them.

SOURCE: "Door Ajar" signal on dash panel stays on even when doors are clo

there should be a switch mounted( or more than one) in the door jamb that tells the car when the car door is open...i will probably look like a little plastic plunger...might be broken off or bad internally

SOURCE: 2003 Volkswagen Jetta Door Ajar Light wont turn off and car alarm

The problem you are experiencing is the drivers side interior light switch is not working. This is usually found in the door latch on later model cars and usually requires the complete latch mechanism changing. However it would pay to check that your car doesn't have a pin switch fitted in the pillar.Unfortunately I think you have the former.

SOURCE: How to remove the door panel of a 1999 Lexus RX 300

You'll need to remove screws that are by the door handle, arm rest, under door and side of door and then gently pull back on the panel as there will also be retaining clips attached and you don't want to break them. If needed, you can pull back the weather seal (can't reuse it, but it's not that important) and you will be able to access everything inside the door