I've been battling with my blinkers on the weekends for about a month now. 
When I started I had absolutely no lights and a faulty switch. I've gotten to

the point where I have all the lights working (including the dash indicator) 
except the front left. I even fixed the switch. My problem is I can't seem to

get the last one to work! The bulb is fine and there doesn't seem to be any 
loose connections. Because the others work, I don't think the flasher unit or

the fuses could be at fault. 

Any ideas?

Also, what is the mystery box behind the panel in front of the passengers 
knees? Could this have anything to do with it?
----------------

are you actually getting juice to  the FL turn signal?   use a test light .
 did you clean up the connections with some sandpaper or a wire brush?   is
the bulb holder faulty?   you didn't mention the year of the bus - the 66 and
67 have a blinker box that everything is routed through - but that is on the
drivers side.  there was no box on the pass side - is it wired to the lights?
  or maybe it's a stereo add- on?   I'd  check the fuses any way.  it doesn't
hurt to clean the fuse block up.

or you could try intoning  :        "electrical gremlins - begone!  leave
this bus!"

:)