This dates way back to the first harness I ever completed for a customer. A friend of mine Caetano who lives a few hours east of me needed a harness for his FC3S and a freshly built 13B. Being an FC guy myself I am pretty familiar with the car and their many electrical gremlins (and apex seals).
The images aren't the greatest but I am still reasonably happy with the results even years later. Some cosmetics have changed but the fundamentals are all still here.
Caetano is running an AEM Inifnity Series 5 ECU, as well as IGN-1A ignition coils. His tuner recommended a decent list of sensors including Fuel pressure, Oil pressure, Oil temp and Wideband O2.
He needed a relay for the Radiator fan and another for the Ignition coils. Made a little bracket that mounted everything neatly and he installed it into the car.
I also built him a Fuel pump relay kit for the larger AEM in tank pump the car was going to be running.