Interior Dome Light Theater Fade Dim

Is anyone aware of how to add the capability of the "theater dimming" lighting to the interior of a car that does not already have it.  As the doors are closed, the lights "fade" out.  I think it may be able to be done with a capacitor of some type, but I have a negative door trigger.

How is that diagram supposed to work if the ground from the "dome bulb" disapears as soon as the door closes? Sure you will extend the amount of time the light has +12V, actually you won't because the domelight probably always has power, but what good is it when the ground is no longer there?

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look at the diagram again dumb sh*t. the ground on the bulb is hard wired(not to a door switch.) it never disapears. when the door closes the relay coil is de-energized which will switch the power from 30 to 87a which is not hooked up. in other words it removes the power from 87. the cap will the hold the dome light on as it drains. this will give you the dimming effect that you are looking for. I did this about 3 days ago, and it works fine. the 1500 uf cap will give you a little over 1 second of dimming on a 194 bulb. (194 is a common size for most dome lights.) if you want a longer dimming time use a 22,000 uf cap instead.

to jc18750 i wonder if you can make a fade in and then a fade out?and bigger loads at 12vdc?