Mk1 Dash Light

This question might have such a simple answer......
What does the red light between the gauges indicate on a MK1 dash?  When I got to work this morning and turned off the ignition that light came on and remained on.  I tried starting the van again, and it started fine, then when I switched it off again it came on again.
 
For the moment I disconnected the battery terminal in case anything is seriously wrong or in danger of shorting out, but I need to know what may be up so I can drive home!

Magoo, you can call yourself an expert after all - I found out you're spot on!
 
I pulled the dash out last night, and on the back of the instrument housing that light was marked "ALT", with the wire colours stamped in to it.  Wires colours matched (so the light was in the right socket) so I went chasing the alternator rather than the oil pressure system.  I wiggled a wire on the back of the alternator (the small light blue one from memory) and the light went out and hasn't reappeared.
 
Cheers!

From memory (without trying it right now) the red light does give a quick flash when I turn it to 'on', and the amber oil light stays on until the van starts - I'm assuming this is right?  The battery doesn't seem to go flat - I've checked it a couple of times with a multimeter.