Tom,
Have just been testing my own system on an 86 Vanagon--turned out my
thermostat was just a bit stiff and was the cause of high readings on
the temp gauge.
My coolant temp gauge system tested at 9.6 volts.
According to what I gathered from the List, this system is powered off
the dash voltage regulator and is 10 volts.  I was getting the 9.6
volts off the wires to the temp sensor in the engine compartment.

Also, be advised that as the engine warms, the voltage will drop as
resistance in the sensor decreases.  On my van, this system is
grounded at the cluster of grounds underneath the coil.
And I assume you know that there are two temp sensors---one for fuel
injection and one for the gauge.

One thing I did to test continuity of the system was pull the
connector from the sensor and bridge the contacts with a piece of
wire----the needle should rise to the top of the gauge.

Dan

On Apr 25, 2008, at 7:19 AM, Michael Vickey wrote:

> Tom, I had a similar problem with one of my doublecabs a year or so
> ago.
>
> The problem was corrected when I replaced the single lead (brown
> wire) to
> the temperature sensor. There was an internal break in the original
> wire -
> not easily detected because the insulation was not broken. You may
> want to
> check the continuity of that wire.
>
> Can't help with the voltage question.
>
> Michael
> http://www.velocity.net/~vickrail/moshevw.htm
>