Wiring diagram by VIN: where to get one, and what the parts catalog adds

Where wiring diagrams by VIN live

Carmakers publish wiring diagrams alongside workshop manuals, diagnostic trouble codes and technical service information, in a repair information portal. Volkswagen Group runs erWin for this. Its content includes wiring and circuit diagrams, workshop procedures, maintenance plans and technical service information, and a new version of the portal went live in Germany in July 2026 and in the UK at the end of August.

The diagram you need depends on the car’s build and fitted options, so have the VIN ready when you open the portal. erWin is aimed at professional independent workshops rather than private motorists, and other carmakers run their own portals for their brands.

The rebuilt erWin puts eight Volkswagen Group brands behind one login: Volkswagen passenger cars, Volkswagen Commercial Vehicles, Audi, Škoda, SEAT, Cupra, Bentley and Lamborghini. For Lamborghini it gives diagnostic information only. Next to the wiring diagrams it carries recall information and control unit data, which the parts catalog does not hold.

Right to repair: who gets access

EU Regulation 2018/858 requires manufacturers to give independent operators unrestricted, standardized and non-discriminatory access to repair and maintenance information. Its Annex X lists what that information covers, and wiring diagrams are on the list next to technical manuals and diagnostic trouble codes.

The regulation also asks for the information in machine-readable form on the manufacturer’s website. Manufacturers may charge reasonable fees and must offer access by the hour, day, month or year. For a one-off electrical job, a short pass to the portal usually costs less than guessing. Our post on right to repair and parts data covers how the rules differ between regions.

What the parts catalog gives you for electrical work

An EPC does not contain wiring diagrams. It shows the electrical system as parts: harnesses, connectors, terminals, fuse and relay carriers, switches, sensors and control modules, each with its genuine part number and the exploded view that places it on the car.

That half matters as much as the circuit. Once the wiring diagram points you to a failed connector or a chafed section of loom, the catalog tells you which connector housing, which repair terminal and which harness belong to that exact VIN.

• Harness part numbers split by options such as a towbar, parking sensors or upgraded audio.
• Connector housings differ in pin count and keying even when they look alike.
• Control modules have a hardware number for the build, and coding follows after fitting.

Why the VIN decides the harness

A wiring loom is built for one combination of equipment. Two cars of the same model and year with different options can take different harnesses, and the model name does not tell you which one you have.

Decode the VIN in the catalog and the parts list narrows to the build. Our post on electrical and wiring parts by VIN goes through connectors, modules and looms one by one.

A workflow for electrical faults

Diagnose with the scan tool and the manufacturer’s wiring diagram, then order with the catalog. Read the fault, trace the circuit on the diagram, find the damaged component and confirm it on the car.

Then enter the VIN in the EPC, open the harness or connector group and take the part number from there. If a repair terminal or a single connector housing is listed on its own, you may avoid buying a whole loom.

Harness and connector part numbers on VINsearch

VINsearch opens 53 official parts catalogs in one browser login, ETKA for Volkswagen Group cars among them. It does not include wiring diagrams or repair manuals, which stay with the carmakers’ service portals. The free VIN decoder reads the manufacturer, country and model year before you start.