Voltage drops steadily to DVD after on

I have an Advent ADV35 overhead monitor/DVD player on the ceiling of a 2006 Toyota 4Runner that plays for 10-15 seconds after it is started and then turns off. I isolated the 12V+ and ground wires and measured the voltage from the time the DVD is inserted and it steadily decreased from 12.8V to about 8V when it turned off. The power and ground wires were spliced into a dome light after a run of about 6 feet. I have never seen this type of voltage change. I bought the car with the overhead dvd player and a "Battery Brain" already installed. The "Battery Brain" monitors the battery, and disconnects power to the car to prevent a dead battery, but only does so when the car is off. While searching for the 12V+ and the ground I found a black box connected, that I suspected to be a relay, but under more research might be a "Devisolator." The "Devisolator" is a device designed to protect a vehicle’s battery from being drained by monitoring the power being drawn by an individual accessory. There are no markings on the black box (2" x 3" x 3") which is connected in series with the 12V wire and ground. Does anyone know what could be causing this problem?

corazon wrote: I have an Advent ADV35 overhead monitor/DVD player on the ceiling of a 2006 Toyota 4Runner that plays for 10-15 seconds after it is started and then turns off. I isolated the 12V+ and ground wires and measured the voltage from the time the DVD is inserted and it steadily decreased from 12.8V to about 8V when it turned off. The power and ground wires were spliced into a dome light after a run of about 6 feet. I have never seen this type of voltage change.

The power and ground wires should not be connected to the dome light wiring at all. That sounds like that's your problem. You need to run dedicated power and ground wires. As the domelight fades out, you're losing your power. Many flip down monitors have their own built in domelights, which you can connect to the factory dome light wiring. However, you need to supply your own power/ground to the unit itself.My ex once told me I have a perfect face for radio.