Right hand side lights not working.

I have a bmw 1992 325i which has an occuring problem. When I turn the lights on, the right hand side indicator, right hand side brake light and right hand side small reg plate light do not light up. But when I indicate or brake then they work. Seems like it has some kind of double circutry that is malfunctioning, strange thing is sometimes it works fine, sometimes it doesn't.

Any ideas guys? I'm going crazy with this one, I'm getting pulled over by the cops daily.!

Thanks,
Chris,