A little tip here for getting a head start on understanding automotive electrical wiring
ELECTRICAL THEORY BY JOSEPH LUCAS
Positive ground depends upon proper circuit functioning, which is the
transmission of negative ions by retention of the visible spectral
manifestation known as "smoke". Smoke is the thing that makes
electrical circuits work; we know this to be true because every time
one lets the smoke out of the electrical system, it stops working.
This can be verified repeatedly through empirical testing.
When, for example, the smoke escapes from an electrical component
(like, say, a Lucas voltage regulator), it will be observed that the
component stops working. The function of the wire harness is to carry
the smoke from one device to another; when the wire harness "springs a
leak," and lets all the smoke out of the system, nothing works
afterwards. Starter motors were frowned upon in British motorcycles for
some time, largely because they consume large quantities of smoke,
requiring very large wires.
It has been noted that Lucas components are possibly more prone to
electrical leakage than Bosch or generic Japanese electrics. Experts
point out that this is because Lucas is British and all things British
leak. British engines leak oil
, shock absorbers and hydraulic forks and
disk brakes leak fluid, British tyres leak air, and the British defense
establishment leaks secrets ... so, naturally, British electrics leak smoke.
>From the basic concept of electrical transmission of energy in the form
of smoke, a better understanding of the mysteries of electrical
components - - especially those of Lucas manufacture - - is gained by
the casual user.