Try adjusting the light itself...if the housing is at the wrong angle it will not work. The angle has to be correct for gravity to take it's effect on the mercury and make the connection when the hood is opened...
My friend got an auto start for her car so she could remotly start the car in the winter and it wasn't working...I traced it to the mercury switch under the hood...The system will not work if the hood is open and the mercury switch was telling the system that it was open...what happened was they mounted it in the wrong place and when the hood was closed the switch was hitting something under the hood and bending...So I had to remount the switch and set the angle and Presto...it worked...