As we said before, I worked on a custom wiring diagram a long time. A complete harness was available from Rhode Island Wire for an Anglia but not for the Prefect which is a little more complicated. Besides, I wanted to add a few features, such as a heater, modern turn signals and courtesy interior lights. The only way I could see to get there was to design and build a custom harness. I started with a very simple A-H Sprite diagram and added the missing features to it. Afterthought indicates it might have been easier to start with an older Jaguar diagram and simplify it as needed. Anyway, with a "final" plan on paper, I contacted Rhode Island Wire to purchase the materials. Although my car has been converted to 12 volts, they suggested using wires for a 6 volt car as they would have a better selection of colors. I liked that idea also because it would mean all the wires would be a little heavier than necessary and better able to handle the current.
I tried to stay as close as practical to the British Lucas color standards although it gets a little sketchy when dealing with non-standard items such as turn signals when there are not enough filaments to handle the task normally. In my case, the brake lights also serve as rear turn signals and the single filament side lights blink as front flashers. This turned out to be a lot of wire and a lot of colors that just can't be found locally at all. When it came, everything was neatly packaged and labeled so there was no possibility of mistake.
I started by selecting a location under the fascia for the fuses and main junction box and running all the wires from there to everything forward. There were holes on either side of the bulkhead that looked suitable for a harness and, it being convenient to do so, I made up a left and right section with only a couple of connections between them. This fed everything except the rear lights, interior light, tag light, petrol gauge and trafficators, at least under the original design. My additions included door switches for the interior light, turn signals and an electric fuel pump. These photos are of the not yet braided left and right front harnesses as they exit through the bulkhead under the bonnet.
With that done, it was time to determine how to lead the harness to the rest of the car. My old scheme was under the body, exposed to the elements, which was not a good plan. After a time, I finally found a plastic tube inside the nearside A post. That had to be for original wiring. The original was probably 4 wires and I needed 9, too many to fit that tight passage. I decided to split the rear harness to a left and right like the front. This meant 10 wires and made me a few feet short on a couple of colors. I also needed a manette harness for the horn and turn signal switches. I could have ordered the individual wires form Rhode Island but it would have been very hard to make without being pre-braided as that tube is a very tight fit. British Wiring had a manette harness already made up and braided that was very close to the colors I wanted so I ordered it instead. I also ordered enough additional wire and some more connectors to finish the job.
With the additional materials in hand, I constructed the left and right rear harnesses and, like the front, taped them every few inches and sent the whole set off to Rhode Island Wire to be braided in black with a yellow tracer. I estimated this well could have been the colors of the original harness braiding for my Prefect. While waiting for the braiding, I decided that switches for a Volkswagen would be ideal for door jamb switches to turn the interior light on. I also got a proper looking B post manual switch off eBay. I cut square holes in each of the door jambs and mounted the switches. These photos are of the dimmer switch harness and the right front harness section passing through the bulkhead.
The 12 volt petrol gauge never worked right, deflecting only about halfway on a full tank, with my 6 volt sender and I never found a 12 volt sender configured right to fit my tank. The answer was to retrieve the original 6 volt gauge and make a voltage reducer to operate it as well as the 6 volt rebuilt trafficators I finally located at Small Ford Spares in England. I also got a Lucas 14W, 2 speed wiper motor from eBay and serviced it. The original wiper switch was a special rotary, off-low-high, unit to park the blades when switched off. My switch is a toggle, low-off-high, unit that I do not want to replace. Another electronic relay box was needed to enable the park function. Finally, my side lights are small and have only single filament bulbs and I did modify my tail lights to have dual filament bulbs. Neither of these will operate flashing turn signals without some outside help. Another relay box had to be designed and built for this function.
I got seriously involved in drawing the wiring diagram. As there are quite a few wires in the system, the master can be a little hard to follow. Therefore, I also made excepts from the master for many of the subsystems. So, If there is a problem with the lighting, for instance, there is a subdiagram that covers only lighting, etc. I had done this same thing for a Jaguar that I rewired for a friend earlier and it seemed like a good idea. The links below are to the various parts of the wiring diagrams and electronic circuit schematics. The following photos are some shots of the braided harness, as received from Rhode Island Wire and installed.