You're right that it's reasonably straightforward but that doesn't mean that it can't behave strangely. As previously mentioned grounds and headlamps are areas that can be confusing and hard to diagnose.
Things that come to mind immediately are:
- I would jettison the original bimetallic 10v voltage stabiliser and get a solid state one. It's very hard to trust/test the bimetallic one.
- A simple mod is to put a link between BR and BP at the cheap/rusty headlamp microswitches so that they operate in parallel - then if either one fails the headlamps keep working.
- If you want the headlamp flasher to work you may have to decide which side of the relay to place the flasher. Generally, on the control side of the relay (low current) they flash slowly while on the switched side of the relay (high current) they flash quickly.
- A minor wiring change is required if you wish to convert to electronic ignition (to accommodate the concomitant tacho conversion from RVI to RVC operation).
- Minor changes are needed if you wish to switch from a dynamo/generator to an alternator - the voltage controller on the bulkhead is no longer needed because voltage control is done by the alternator itself.
- Most modern high torque starters have their own built-in solenoid, so if you wish to use one you'll need to decide if you want to dump the original bulkhead solenoid or keep it so that you run both solenoids in series (this is actually useful because keeping the solenoid on the bulkhead allows you to turn the engine over on the battery while the ignition is off).
- Finding a turn signal flasher unit that works at all (reliably, at a consistent speed, and drives the tell-tale in speedo/tacho), let alone with LEDs, and makes an audible sound, is an interesting/fruitless exercise.
- If I were starting from scratch I might lay in wiring for an electric fuel pump in case I want to install one someday.
- There are surely other items that don't come to mind right now.....
Also, I recently found this in a response to an article in a recent Hagerty newsletter. It seems useful to me.
Nick
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By Dave Braun:
The British wiring codes are amazingly simple and easy to learn. Brown is power, black is ground. After it is switched in the ignition switch, Brown becomes white. When White is fused, it becomes the green wires, and when Brown is fused, it becomes the purple circuits. When Brown goes through the headlamp circuits it comes out as Red with Green stripes for parking lights, which do go through the fuse block and come out red to go to the lamps, and red with a white stripe to go to the dash lights., and brown comes out of the head lamp switch as blue for head lamp dip switch. blue with white stripes are main beam, and blue with red strips are dipped beams. Any wire that has a black stripe is a typically a switched circuit ground (like a lot of negative side two wire horn systems) and green wires tend to feed the convenience things on the car. The yellow wires are for the alternator or generator. There are more, but armed with this info you can troubleshoot almost any system on a British car.
Grounds are the big problem, keep them clean and assemble them with silicone dielectric grease. the little bullet connectors throughout the car need to be likewise cleaned and assembled with dielectric grease, and check to make sure the heat hasn?t overcome the springback of the metal for the secure connections. Some of the weaker contacts in the switching can greatly benefit from having a simple 12 volt relay placed in the circuit to take the electrical load and heat off the switches. Although early British cars typically have two fuses for the entire car, and the later ones have four (up to the early eighties) the electrical systems if properly cared for and kept in good order are almost bullet proof.