[Vwdiesel] TDI electrical weirdness

[S. Shourds]

This will show what I don't know about electrical work.  The TDI is dead 
again, and it's the same electrical mess as last time.  The end result 
is that there is 12V going in to the ignition switch and only 5V getting 
out to the D15 (for those of you following along at home) terminal that 
powers things like the instrument lights, door locks, etc.  Makes it to 
where the car will crank fine but won't start, among other things.  I 
can measure the 12V going in and the 5V coming out.  There's no weird 
back current that I can tell.  Last time I went through this, I looked 
at every ground I could find and found them all good and I tested the 
voltage against the frame.  What fixed it last time was a new ignition 
switch.  I have a new one on order but I'm curious as to why this 
problem would be.  I can't think of any good reason why that voltage 
would vanish.  Particularly when the switch in the car is less than 6 
months old.  Makes me think I need to have a spare switch in the car and 
leave the steering wheel shroud off.  I need to get my '65 MB 190Dc 
running.  Even the starter selenoid is mechanically operated.  So, 
anyone able to enlighten this mystery?

-Shalyn

-00 Jetta TDI:  dead
-85 Jetta TD:  dead
-08 Chevy Cobalt rent car:  makes life not worth living