Before you start going through the elaborate process of tracing wiring and
looking for shorts, etc.etc.  I really suggest that you just try to replace
the sensor, or borrow one from someone else's VW (any will do--if I were in
geographic proximity I'd lend you one from my Passat or Bus).  Anyway, it's
cheap, and it certainly solved the problem when it happened to me.  I
suggest that many more things can happen to this sensor in terms of it going
out than could happen to anything behind your instrument cluster (although a
brake fluid spill back there could be disastrous).

It just appears to me that we rush into the worst possible scenarios
sometimes when trying to solve each other's mechanical problems.  The
process should be from the simple and cheap to the complicated and expensive.