The Circuit Diagram Project
The XM is a complicated beast when it comes to electrics and electronics: there is no denying that. It entered the executive car market with practically all the toys of the era. There are billions of components, thick harnesses, a plethora of connectors, everywhere. Finding anything without the proper diagrams is nigh impossible.
The factory manuals have all the diagrams for sure, as well as after-market manuals like Haynes in the UK or RTA in France. But they all reproduce the factory schematics that, still before the fully computerized era, were drawn traditionally, and for obvious cost reasons, in black and white (although the layout diagrams made use of the red spot print color already available because of the Citroën logo).
The diagram booklet we offer promises a little bit more. Although based on the original manuals in layout and many details, it uses color to help understanding. Parts, although they also indicate the factory numbering scheme, document themselves directly on the pages, without the need for constant cross referencing. Wires and connectors are color coded instead of cryptic literal abbreviations. Usual automotive icons help identify every important part. Harnesses are displayed in an unobtrusive light type that's available when needed but doesn't really get in the way when not.
Layout diagrams not only show the actual location of the component but have added clarifications whenever possible about precise whereabouts (LHD and RHD, where applicable) and various other pieces of information like bulb types, diagnostic codes and similar. Components use the usual icons to quickly convey their purpose, often without the need to cross reference to the numerical identifiers of the schematic diagrams.
The diagrams show a fully loaded car, with all the usual engines (diesels, petrol 2.0 and various V6 versions), Mark II, as a good starting point for most cars in use. And the diagrams underwent numerous small modifications during their years of use in the XM community: inevitable errors and omissions of the original factory diagrams were corrected, based on the actual cars.