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!

I am no expert , to me it sounds like the alternator light is the red one to indicate you have charge issues , not saying you have but you might have awire to the alternator the wrong way around to a constant current ????????? my thoughts only
Magoo

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!

Dude
 
One thing to watch on these is that when you turn the key to "on" is that you do need to see a red light (alternator / charge lamp).
 
Mk 1's run the charging circuit through that lamp. Dumb idea really but if the lamp blows your battery doesn't get charged.
 
Cheers
 
Shaun B
 

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.