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