I have a 2004 Ford excursion eddiebauer v10 my back up sensor light warning light will come on when truck is in reverse will reset occasionally but always returns to fail mode what and where should I do to fix this problem last time the mechanic told me that the liscense plate bulbs needed o be replace because they where not wroking and the share the same circuit checked them and there are both fine Please help wife loves this truck and needs sensors to work beep chirp to get in and out of tight spots