How do you tackle under the dash with the dash all together? Do things need to be taken out of the dash to have room to work under there?
The first thing to do is take the seat out. Then build a small plywood platform that extends the floorboard far enough to lie down comfortably and work under the dash without turning your back into a pretzel. It's a lot easier to do accurate work if you're not in pain.
Then try not to go to sleep!
Jerry