Have you inadvertently let the smoke out of the wires on your classic British car? This, then, is the solution to your problem!
While reading up about “magic smoke” — just type it into Wikipedia for an explanation — I discover that the concept predates the invention of the silicon chip. In fact, smoke was an important part of the wiring harness and electrical systems of most British cars of the 1950s and 1960s.
Do take some time to read the Q&A section. Much would not disgrace a Goon Show script.