I might be able to help if you can indicate what year headlamp you are using. The 1928 and early 1929 headlamp used a conduit only large enough for two wires, and the sleeve in the opening at the headlamp base was only large enough for a two wire conduit to attach. The rest of the production thru end of 1931 used a larger conduit for three wires and the headlamp base wire opening was larger to accommodate three wires.