Lets look at this carefully, Nah lets just fix it.
This is the list of items coming from Fuse #1 in the fuse box.
Center consol illimination
Lights Park/Tail RH
Lights Marker/license
Warning Indicators/instument cluster illumination
Warning system.
Sound like you
So check to see if all these items are inop.
If so its the #1 fuse, replace it, If still a no-go then its wire harness time.
Wire harness.
The diagram shows from fuse #1 A GY/RD wire goes to the light switch. check voltage at the back of the light switch at the GY/RD wire.
From the light switch GY/VI goes to the warning system relay and the LH/RH license light. Check votage there
The GY/VI wire also goes to the instument cluster for illumination and to the center console upper section. Also the wire goes to the radio and cigar lighter then go ground G102 (Behind center of instrument cluster)
It is this GY/VI wire that goes to the rheostat. So if no power there, then we work back to the fuse. (You have checked for voltage on both sides of the fuse, correct??)
The only thing left besides the wire is the light switch . Use the ohm meter and make sure it is working correctly. You may have burnt out a contact with the switch rigging.
Switch contacts
From the fuse to the switch GY/RD wire to contact N30 (or M30 hard to read) The output ( the GY/GY/VI wire, as the manual shows it) is contact K. so check continuity with the switch ON from N30 to K.
http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/ETM/123%20turbodiesel_2.pdf
page 121/4/5 and is the complete diagram for your problem.
Dave
To add, the wire does continue to the window switches from the instrument panel to the switches as a GY/BU wire to the C124 distribution block then as a GY wire to the switches. So there is a connection between the switch rigging you did and the circuit.