This is an in depth, instructional manual that describes most vehicle electrical systems from base principles.
The writing style is very clear, though some of the pictures are difficult to interpret.
Unfortunately, some of the information needs updating. The published date is 2006, but the text occasionally refers to the 1990's in the future tense and some of the illustrations are not relevant to modern vehicles. Statements such as 'All batteries need regular maintenance, topping up with de-ionised water' may have been true in 1981.
That said, ECU's, common rail diesel engines, glow plugs and engine management are well covered and include vital post 2005 information.
Knowing very little about vehicle maintenance, I have learned a lot from this book and have not found a better introduction.