If the above suggestions don't do it, I'd also take a look at the wiring diagram for the year and make sure the switches are actually getting current to them. Then if so, that switch contacts are clean.

The outside of bulb housing is the ground area on bayonet type bulbs that have the brass can on the business end. Also may need to very gently dress the contact tip on bulb housing, like polishing it smooth & even, however it's not but lead & zinc so real soft.