the head, interior, and brake lights won't come on--HELP!!

We have checked the switch, and it didn't look burnt or anything so my husband doesn't think that's it. All I really know is that for them to work I used to tap on the panel near the switch and it would flicker back into existence, which is where the switch is located. My husband doesn't feel that it is the switch though because we are getting NO lights whatsoever. It used to flicker, now it's none. He thought it might be getting "grounded out" but I have no clue how he can check for that either.

Thanks in advance for your time!

-Kim-