The Scion xB is equipped with a dome supervision function which turns on the dome light when you use the keyless entry, turns off the dome light 15 seconds after the doors are shut, etc. I installed a flip down monitor and tried using the dome lights which were built into it. I hooked up the continuos power, door switch, and ran a ground. The only way I could get the dome light to work was in the ON position, the DOOR postion would not work. So, I reinstalled the factory dome light, and it still will no longer work in the DOOR position. I have checked all the fuses, checked the wiring, and still nothing. It was suggested that I disconnect the battery and let it sit in order to discharge any capacitors and I have done that with no success. I would use the Toyota tech service, but they charge $50 a month to use it. Does anyone have any ideas? Does anyone know where the dome supervision module is located? I have seen the wiring diagrams, and it says where the door trigger wire is, then it says for dome supervision use door triigger. I disconnected that plug from the fuse block and it didn't help either.
I hope you bought the flipdown screen with replaceable dome lightbulbs. Usually with the irreplaceable domelight bulbs built in the flipdown screens has it's own circuit and it does have an effect with the delay domelight with your xb. I won't name the company but it has the same problem with the Toyota Sienna with a delay domelight. However, many high-end flipdown screens should not have a problem with a delay domelight.
Refer to the owners manual of your mobile video screen how to connect the domelight to your xb. Your XB is probably negative trigger or positive trigger.
If you have done what it said in the manual, try the dimmer switch. Experiment by turning the dimmer off. Usually it works.
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As far as the wiring diagrams go, the xB has negative trigger. I just went and tried the dimmer switch with no success. It doesn't dim the dome light normally anyways. It seems as if something got burned up somewhere. Any more ideas?