After pulling out the 60 year old wiring harness from under the dash and looking at the condition of the connectors I was surprised the car hasn't caught fire yet. The old harness connectors were dried out and cracking and the wires were stiff as if they lived their life under the hood. The main power wire at the ignition switch was hanging on by only a few strains and a portion of the fuse box was missing leaving wires exposed.
The wiring system was replaced with model specific reproduction harness. This includes headlight feed, engine feed, under dash, headlight extensions and the harness going to the rear of the car. I made some required changes to the harness since I will be running a V8 with EFI instead of a carburetor six cylinder. I also have one-wire alternator with internal regulator instead of generator with external regulator. While I had the a couple feet of the harness unwrapped I added a wire going to the alternator for the dash idiot light if in case I change over to a other style alternator. I also added an extra 12 gauge wire from the starter solenoid to feed the headlight relays. I ran a 6 gauge wire to feed the cooling system relays and MSD box. I had to unwrap the harness on the firewall end about 4 inches to get wires to exit the harness more closer to the brake light switch also since the switch is in a new location. I added an extra fuse block under the dash to help carry the added electrical load. The Atomic EFI has its own dedicated power and ground coming off the smaller wires on the battery cables.
Since I replaced the steering column back in the early 70's with a 65 Mustang column after cutting the tube to the correct length and replaced the wiring connectors to plug into the harness, the new turn signal switch did save me about $10.