[Vwdiesel] 89 Jetta D phantom voltage update

[Just Joe]

Of everything you've said... 

"...When I applied the brakes, the volt meter jumped to 12.80 (max battery 
voltage). Got the same voltage jump when I switch on the headlights or the 
radio. ..."

Makes me wonder about your brake/tail light bulbs.  Buddy of mine told me
once that for certain years of Jettas (ever since they've been made in
Mexico I think) that you HAD to buy VW bulbs.  Something about the German
engineers decided to eliminate a wire somewhere by inserting a diode in the
bulb itself.  Regular auto parts store bulbs cause issues... One of the side
effects of not using VW bulbs is your brake lights are always on.  (again,
this is second hand knowledge as I don't own a Jetta)

Hope this helps...

Joe