The CANBUS is desgined like a network as mentioned before. It is used to help reduce the bulk of wiring needed to the mostly "analog" devices such as a motors ( washers, heater fans, door locks, etc.) or illumination.
A good example is your dome light.
In a regular car, two things activate the dome light: door and second switch.
The second switch, usually next to the dome light, is easy enough. Power comes from fuse box.
The door switch would be the same in a conventional car. It runs from the fuse box, which is probably close by on the driver side, then runs parallel to the dome lamp with the other 3 doors. That's a lot of wire to run from EACH door jamb to the dome light. Effectively, you have 2 wires with +12V running through the frame.
Now in a CANBUS, you have only (1) 12v wire going to the lamp. You have all switches using much smaller gauge wires going to (guessing now) a switch controller. These wires don't carry much more than a few volts and much less amperage (milliamps.) The switches as mentioned before now are like "jumpers" telling the switch box what to activate. In this case the dome light.
We didn't reduce the "number" of wires, however, we did reduce the bulk, not to mention the +12V with higher amperage that "could" possibly short out due to vibration against the chassis as the car ages.
This in fact is the same type of wiring I used in SNKVNNM. The system is CANBUS based so I now run 50% less wiring in the FFR, NO relays whatsoever, and 99% of my switches do not carry 12V. If I short out a wire, something might operate on it's own will but it won't short out and cause a fire behind the dash.
HTH. I don't know what on a B5 or B5.5 is controlled via CANBUS but it is there.
I suspect the VW may work much like the I-Squared system. The I-Squared Engineering (ISQE) system utlizes a 2 part or 2 box system. The Master Controller, where all switches go to, and the Power Controller, where all power emminates from.
All of my dash switches, inlcuding the thermostatic radiator fan switch , is tied to the Master Controller. All of the wires are no thicker than what you'd find in a CAT5 network cable. This box contains nothing more than a set of micro processors that talk back to the Power Controller using a 15 pin Computer Cable that you can buy at an electronics store. This is the main "bus" if you will of communications.
The Power Controller contains microprocessors as well and does many things: it talks back to the Master Controller to ensure they are in sync, it monitors voltage across all of it's fused circuits, ensuring voltage is consistent and tries to prevent under and over loads. The Power controller contains MOSFETs which essentially replaces all relays you would nomrally have wired behind the dash. This is the key to reducing the wiring. With both boxes telling what to power on/off, wiring to the end-points is just that: Wire between fuse box to lamps/ignition/fuel pump/fans/wipers/park lights/gauges/ etc....
I can tell you this, when you pull your own wires it is crystal clear what the advantages of this kind of setup is. I wired my entire car probably in just 2 days of total hours ( 48 hours ). The hardest part was cutting the aluminum panels to route the primary computer cable from behind the dash to the rear of the car. After that, wiring was pretty damn easy!
I don't know. CANBUS is more of a concept or possibly a standard. Implementation, well, that's different I suppose. I don't know how invasive their system is. In the 98's, they still used relays so I think they were just testing a few things to see how it worked. I believe they used them on the rear tail lamps and maybe the dome light (ever notice it turns off slowly? No switch I know of does that.) But don't quote me on that. With drive by wire being more prevalent, I can see this being used more and more. But it's also a scary thing too. A very strong EMP could make your car do things you didn't intend it to do. I know, that's science fiction like, but sh!t happens and you never know.
CANbus - Controller Area Network bus , "bus" here being a electrical conductor or network media. http://www.canbus.us/
A digital bus system that is used for information exchange and control, particularly in automobiles. Equivalent to a network (like ethernet) in the office environment.