Today I finished the rewiring of the 50. What a job, I did it without taking out the dash finding it very relaxing working on my back feet up in the air on the seat. I worked a little at a time when I got tired I quit. Part time it took me about 3 weeks to complete.
Lessons learned...
Remove the heater distribution box from the heater and firewall.
As others have said drop the heater controls.
Remove the two hidden special nuts holding the switches to the front fascia.
Disconnect the cigar lighter, the nameplate illumination light, and the Headlight indicator light from the switch panel.
Now you can pull the switches back from the from the fascia.
Remove the radio next. It is easier to work underneath when the radio is out.
Remove the front fascia. To do this there are two flat head bolts over the ash tray and one over the hole that the radio fits into. Next remove the one Phillips bolt under the radio that holds the bottom of the dash to the face plate. Next remove the small Phillips screw that holds the bottom of the ash tray opening to the dash. The headlight on light is attached here.
Lastly, notice that there are two very small Phillips screws at the top of the radio grille opening. These hold the face plate to the dash.
There is a metal bar in the opening that the ash tray rocks on. You may have to work that out before the face plate will come out.
Carefully work the face plate out of the opening.
Now you have a way to get your arm into the space behind the instruments.
Remove the nuts holding the harness to the instruments.
Carefully disconnect the switch panel from the harness.
At this point I cut out the harness severing it at the firewall as I was not going to reuse it.
I worked out the harness through the opening I had created by removing the switch panel.
I took the old harness indoors and cut it apart as I used the wires that were only behind the dash as patterns for the new wires.
Using the wiring diagrams from this site I duplicated the harness carefully labeling each wire on each end with the numbers from the diagram. I did that as it is impossible to get all of the proper colors in cloth covered wire and I wanted to use cloth covered wire for period correctness.
I cut the wires that pass through the firewall long and cut and attached them once the under dash work was done.
Before I buttoned up the dash I checked each circuit with power to ensure things were right. Good thing too, as when I rewired the turn signal to switch socket I misread the diagram ans wired it from the rear and not the front, so nothing worked right. I had to open up the socket and solder the connections correctly, now it works right.
Finally, I tied up all the wiring using tie wraps and reinstalled the components in reverse order.
Ran the car for the first time in a month today and everything works as it should.
