Idiot Light Definitions?

[Lokkju]

I have a 1987 Audi 5000S Quatro, but I don't have the user manual. 
For some while now, I have had a idiot light coming on (same location
as the brake pad warning light) that looks like a circle with a square
on top of it, with a "X" through it.  No idea what this light means -
anyone?

On an unrelated topic, yesterday my car DUMPED all of it's coolant.  I
immediately turned it off and checked all the hoses and stuff.  I
eventually found that there was a small plastic peice that had come
apart (not broke - just come apart).  It was on a coolant hose that
was right behind engine block - anyone know what this is?  it looks
almost like some sort of pressure sensor...  I simply glued it back
together (with gap-fill epoxy), and put it back in.  It does not leak
now, but the engine is overheating FAST - 5-10 min.  My next step is
to check if water is flowing freely through all the coolant hoses, but
I would love some input - thanks.

Nick
lokkju at gmail.com