Courtesy lights stay on all the time, only go out by pulling fuse

The courtesy lights work on a relay/switch to turn the lights off 15 - 30 seconds when the doors are open then closed. If the relay is staying to cold then it cannot heat up to break the circuit to the courtesy lights. I would first try replacing the courtesy light relay and if that fails to solve the problem, the switch may be the faulty candidate.

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

the courtesy and dome lights are operated by switches in the door frame look around the opening and look for a small black button
that button presses back in and breaks the circuit thereby putting out the light
if it is earthed ( grounded) at the back then the lights will stay on
there is one for each door and any one will keep the lights on

No other lights on ,dome, courtesy etc...
Battery Rundown Protection/Inadvertent Power
In the event that any of the interior lamps supplied voltage by the inadvertent power relay and ground from the courtesy lamp relay were to remain on when the ignition is OFF after a period of 20 minutes, the BCM will deactivate the inadvertent power relay turning OFF all of the lamps on that circuit to prevent total battery discharge. Only when the ignition switch is cycled back to the RUN position will the BCM reset the internal timer and reactivate the inadvertent power relay. When the inadvertent power relay is not energized, the BCM utilizes the inadvertent power courtesy lamp supply voltage circuit to monitor for a courtesy lamp switch request signal. If a courtesy lamp switch is activated, the BCM will receive the signal to energize the inadvertent power relay by grounding the control circuit.
It maybe your radio !
It may

it sounds like you have somthing staying powered up hook up battery negitive cable and then use test light on positive lead put clamp on battery positive lead and use the point on the battery if light is on bright then you have somthing staying on like glove light dome lights or even visor lights with lead still hooked up you need to touch the clamp to the point end to power down the timer system usually 20 seconds then pull clamp away from point end while staying connected with battery and cable if you loose that connection you will need to start timer power down again then while someone is keeping the connection pull one fuse at a time and notice if light goes out or dim if it does either then see what that fuse powers and it will tell you what is staying powered

some dimmer switches control the time the interior lights stay on and for how long

in the door jam you have aswicth, myte be cover with
rubber skin remove the rubber and unsrew the little
switch and replace it with anew one start with driver
door its the most used ( remove fuse first)

Have you tried the switch on the dash that turns them on? Are door switches adjusted properly?

Is it an old van? Can you see on the door frame a switch does it come out when the door is opened (push in and out a few times). 3 position switch on always / off always and door switch?

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.