Hey Napman,
     Did you check the grounding connections behind the fuse panel?  There
are star like connections that bring several ground wires to a common tie
point.  I have had trouble with this connection getting wet from a window
seal leak ( see archieves).  I lost several devices because of this, one was
the headlights on a winding road in the ozark mountains.  Check to see if
there is any corrosion on the connections or burnt wires.
     Hope this helps.

Colin Moran