lights don't always work on heater dials

Hi, I have a Ford fiesta 1.4 tdci 08, the lights behind my heater dials I.e the heat selector, fan speed setting and position dial, don't all always work, some will work, then some won't, if I bang the side some come back on or they go off, or all come on, I'm guessing it might be a dodgy connection, anyone have any ideas what else it could be or has anyone experienced this type of thing before, any help would be appreciated.

Thanks!