Tracking down a short

You should be able to SEE that on the light. Before you yank the alternator, take your light and put it from the alternator output to the wire which normally connects there, and if that "is" the drain, the lamp should at least glow.

It also disturbs me when you say, you pulled fuses, etc, and the "lamp got dimmer." An obvious dimming of the lamp should indicate a drain. BE SURE you do not have something (a switch) "on" that will enable a drain, or that the brake pedal is not depressed, and PUSH THE DOOR SWITCH in!!! LOL.

It also may be that you somehow have more than one drain, it could happen

(I'm not familiar with newer cars, it just might be that some of them have magnetic door switches instead of the old mechanical kind. In this case you would have to close the door and wait for the lamp delay for each test, or figure some other way to disable it. Removing the dome/ courtesy lamps may NOT remove all the drain because these may be controlled by electronic modules. My 98 Ranger has such a module)