I started in on the electrical system in earnest today. The first problem to solve was where to mount the fuse box.
There are competing goals here, first place it so that over all installation is simplified, second is to place it so that the fuse box can be reached easily to change fuses. These goals conflict. I ultimately decide to go for ease of installation, and settle for having to remove the entire scuttle and windshield to get to the fuse box if necessary. That won’t be tremendously difficult, and it will make me think before just rushing in to change a fuse (they shouldn’t ever blow anyway!)
The second real problem was controlling the blinkers. My car will have a single two filament bulb on each side in the rear. One filament will act as brake and directional signal. The trick here is that the blinker gets priority over the brakes, meaning that the if the blinker is on and the brakes are on, the correct lamp should blink rather than be solid, the opposite lamp should show the brake signal. Since the blinker signal isn’t constant you can’t use it to to override the brake signal should you be braking while the turn signal is active. Production cars handle this by mechanically mixing the two signals in their turn signal switch on the steering column. I don’t have enough room between my steering wheel hub and the dash board to place a production turn signal switch so I had to build an electronic mixer to take input from a ON-OFF-ON double pole switch mount on the dash.
The mixer consists of two double pole, double throw relays that mix the brake signal and the turn signal and allow independent drive of the forward flashers and dash indicators. Here is the Turn Signal Mixer Schematic. The parts can all be found at Radio Shack (yes they do still sell electronic components and not just cheap stereos and cell phones).