Installed cree leds in my dome and map lights. After a few days, I noticed a faint buzzing noise. Traced it down to the newly installed leds. I guess I didn't notice the sound before because I'd start the car immediately or the ambient noise was high enough to drown it out. There was no buzz with the door open or when the switch for the light was in the on position. So, what happens is when the door is shut, the voltage drops to around 5 volts. These leds did not like that amount of voltage drop, and the driving circuit for the led would start to buzz. Although the led still functioned. I put the incandescent bulbs back in, but the voltage still dropped to 5 volts. So it wasn't a load issue. The bcm, gem or whatever Subaru calls it must be the cotrolling factor. I tried a 3528 smd chipped light, it did not buzz with the lower voltage and it did stay lit. But I did not like the color. Too blue, made the interior black and red colors look faded out. So I was determined to get the cree led light to work without the buzz. The cree has good color IMO, white with no yellow and barely, if any, blue. So I found a dc to dc converter. A 12 volt regulator wouldn't work because you need to maintain a minimum voltage a few volts above the 12 volts.
Remove the dome light lens by putting your fingers of both hands on the trunk side of the lens and pull down. Then remove the fixture from the head liner by removing 2 philips head screws. You can then remove the plug by pressing down on the tab. There are three wires, blue +12v, green with yellow for the "bcm" controlled ground and black for the ground. Cut the blue then the green wire from the plug. Do not cut these wires at the same time, do one then the other or you could short the circuit out and blow a fuse. Leave enough wire in order to splice on new wires for extensions. Do not allow the stripped wires to touch. Splice on about a 10" piece of wire. Attach the wires, not the connector end, blue wire to the IN+ and the green wire to the IN-. Attach wires from the OUT+ (blue) to the blue wire on the connector plug and OUT- (green) to the green wire on the connector plug. Tape all connections as you go. Connect the plug into the light fixture. Next, you will need to adjust the output voltage of the dc to dc converter. Place the voltmeter leads on the tabs of the light bulb holder. Open the door and adjust the dc to dc converter for 12 volt. This is done by turning the potentiometer on the board, counterclockwise to lower voltage. Then use a double layer of double sided tape on the back of the board to secure it to the top side of the headliner. I secured mine about 5 inches to the driver's side, so that it would clear the sliding sunroof shade. Next will be the map lights.
2X CREE 5 Watts 6000K LED White SMD Map Dome Interior Lights Bulbs 31mm Festoon | eBay