All of the wiring, and most of the electrical components, were supplied by Lucas. When it comes to current capacity of the wires, very little “safety margin” was built into the system. It was capable of doing its job, but not a lot more, so it needs to be in tip-top shape.
If you see lots of little red, blue and yellow “crimp” terminals and strange wiring additions (red wire for electricity!), you have evidence that someone has done some creative repairs, usually bypassing problems that would have better been repaired correctly. Look for burned or melted insulation or tape. There are many ways an amateur electrician can cause shorts while trying to install a radio or the like. If you see evidence of this kind of work, you may be in for a new wiring harness or several hours on your back under the dash making things right.
Not all changes are bad, however. Some modifications can be improvements, such as the addition of relays to drive the headlights, upgraded alternators or gear-reductions starters. Some are simply repairs, such as the replacement of a broken or corroded terminal, and if done properly can be left in place.
Check all of the switches. Do they all operate their respective devices? Do all the gauges work? Have they been replaced with incorrect or generic parts? Are there extra holes in the dash or console? Ominous!
One of the prime reasons that Lucas electrics have a bad reputation is the use of “bullet” connectors wherever two or more wires are connected together. Inside each little rubber connector sleeve is a steel tube that can corrode and cause poor or intermittent connections. The bullets on the individual wires themselves are either crimped or soldered on at the factory, and are usually fine. Any corroded sleeves should be replaced. If one were to simply spend an afternoon replacing every one of the sleeves on the car, the wiring would most likely behave just fine for another thirty years.