This thread will track the installation of a Painless 20120 wiring harness in my ’65 Mustang Coupe. The intention is not to detail the entire installation but rather to highlight some of the problems I ran into, or mistakes I made. Let’s just say, before I start, that I’m not an electrical wizard. My car is a rolling shell at the moment. The entire dash is stripped out. Ok lets go. 1. Before I started I did examine the contents of the harness kit and verified that I had all the separate parts per the parts list. I also examined all the connectors to verify that they were good. I did this so that there would be no surprises when I got the thing under the dash. This turned out to be a good idea as I found a cracked connector. Rather than return the harness, I chose to replace it. 2. Drilling the 1.25 inch holes in the firewall for the pass through plates. This wasn’t as easy as it sounds. I used a hole saw, but the task was to open up an existing rectangular hole. There wasn’t any material there for the pilot drill of the hole saw, so I ended up having to screw a block of wood to the interior of the firewall, using some existing holes and use that for the pilot drill. 3. Installation of the pass through plates on the firewall. Painless do not supply a drill template. My advice would be to make one. In addition for the large square plate, one of the corner holes coincides with the sloping part of the firewall (see attached photo). It was difficult to drill and install this screw. It may have been better to drill another hole in the pass through plate in a more suitable position. Access to drill any holes was very tight on the smaller pass through plate between the drivers fender and the and brake MC. I had to remove the MC. 4. Painless has advised me that it is easier to insert the harnesses through the pass through plates before the plates are screwed to the firewall. 5. Installation of the new fuse box base plate was very difficult. The mounting hole pattern is different to the existing fuse box. Painless do not supply an adapter plate. It was necessary to drill mounting holes for the new fuse box under the dash. This was very difficult to access. Again Painless do not supply a drill template. My advice would be to make one. 6. Finally mounting the fuse box to the mounting plate. Look at the photo in the instructions. The harness is supposed to exit from the top. I was tired and (stupidly) installed mine upside down, it’s not fool proofed. It was a pig to separate the fuse box from the base plate. I had to make a tool to bend the four plastic tabs to allow the two to separate. 7. Next week I’ll start the routing. I’ll be using Painless Powerbraid sheathing. I’ve already bought a bunch of good quality tie wraps. More later. Any other comments from people with experience of Painless Wiring harnesses would be appreciated.