I believe there is an In Line Fuse in between the Wiring from Bulb contact to connection on Bulk Head. I would suggest using a light tester probe under hood lite by removing bulb, with Hood up touch Light tester probe on the mercury switch and see if it lights the tester, then check in line fuse 1st.
Is this a Custom Model? They came standard with the Light Group.
Good luck with your project.
Doug