Most repair guides for common British cars worth their salt have wiring diagrams included to help you identify the multicolored freeway system of wiring in your particular car. Simple black on white diagrams with color/tracer keys are very useful, but for you visual learners, a color diagram is worth the price.
The folks behind Advance Auto Wire have taken the time to render a colorized version of the diagrams for MGB, MGC, MGB V8 and Triumph TR models through TR6. They are in pdf files so you can print them in large format for easy reference. I would recommend bookmarking the relevant pages for future reference.