Hmm... it looks like you can tuck the wire in the channel between the shelf liner and the window. Run the wires towards the left b-pillar then floss it between the speaker grill and sail panel. Tuck the wire between the seat back and wind lace all the way to the floor. Pry off the door jamb liner to get to the brake wires to the trunk. No drill, probably just a putty knife to push the wires beyond sight. Look for the wires that match the color of the wires at the brake lights.

Sixto
83 300SD can be yours
98 E320 wagon