I've been known to use a step stool and a piece of plywood about four feet long and 18" wide to help me do under-dash work, or even take the seat out if I'm going to be there awhile. For some reason, it's a lot harder to get a 70 year old body under a dash than it was 40 years earlier! It sounds like you need to do some circuit tracing from the "accessory" terminal of the ignition switch to the fuse block, then to the wiper switch, etc. I always start at a place I know there's voltage, and follow the wiring through whatever fuses and switches are involved to find where the circuit loses continuity.
Jerry
