I have a after market 7" DVD/GPS unit, wired the red power wire to cigarette lighter wire which is a rally of ignition power, yellow wire to battery. Every time I start the engine, the DVD unit's light flashes (that is odd), it keeps flashing but after about 5 minutes, the unit stops working. Could not figure out the problem. Any guess? Incorrect wiring? or maybe the unit is a defect? thanks.