I know I am late to the party (just found these forums), but have you checked the lights themselves? The wiring of the house exterior lighting is very cheesy, and one by one the lights will fail due to a bad connection.
The wires for the clearance lights come up the left corners, where they branch out for the front and rear legs across the body. They used push-connections, where there is not a lot of contact pressure on the wires and the slightest bit of corrosion causes failure. I would start at the tail lights, and check for voltage at the wire itself coming into the housing. If present, use a sharp probe to push down on the metal strip where the wire connects to the light. This will work in the meantime, eventually you will need to change all the clearance lights out for modern units (LEDs look nice on these Minnies), and clean up the wiring to the taillights.