[s-cars] boost gauge install

[Jerry Scott]

I have almost completed my pillar post gauge install, but can't seem to 
find a power source for the light that has the dimmer control.  There 
are several places that I can get 12v, but not the potentiometer control 
for the dash lights.  I have the knee panel off and the door jam fuse 
panel dropped.  Any suggestions on where to tap for this power.
Jerry
93 S4