Hey Jim,

My copy Bentley indicates that the light signals low coolant AS WELL AS
excessive temterature.  I found this to be true a few months ago when my
coolant light went haywire.  At first, the guage stayed normal, eventually
it would peg as soon as I turned the key.

It turned out that the wires going to the temp sensor (thermostat housing)
were shorted to ground on a piece of the frame.  Apparently, the wires were
rubbing against metal, shorting intermittantly, not long enough at first
for the gauge to react, eventually wearing to the point that they were
shorted all the time.

I also saw the light go on once when I tried going over the Beartooth Pass
(15,000+ feet) with a seriously overloaded van (coolant level was OK, just
very hot).

Maybe the light function is unique to the '90 and up vans, I haven't
studied the older wiring diagrams.  My van, for instance, doesn't have an
O2 sensor light, speedo cable is one piece wheel to speedo.

Dan Fuller
'90 Carat