Tara,
I wasn't able to locate a diagram in the Coach Assist library. Are you trying to find where to get 12V to the dimmer or where the dimmer signal goes after it leaves the switch? If the former, you should be able to locate the wire that supplies 12v to the dash lights (in an 02 Marquis, the wire is #63, but may not be same on your coach). In any case, locate that wire and attach on lead of an ohmmeter. Probe the leads coming off the dimmer control. One of them will show varying resistance when the control is turned. Connect that wire to a 12v source and the lights should work and dim.
If none of the dash lights work check to see that you don't have a blown fuse.
Steve