OBD2 Cable: Connect & Diagnose Your Car

hello everyone,

Before you tear me apart: Yes, I did read through old forum posts.

Despite this, I have the following questions regarding two problems:

Problem 1: Connecting VAGCOM and Digi-Prog software on a laptop to a Golf and Audi using an OBD interface (let's call it a 'link cable').

- Which instructions can you trust with a clear conscience?
I am an experienced electronics technician with nearly 'unlimited' capabilities for etching and assembling printed circuit boards (including, and especially, SMD components).

There are many guides available for this 'link cable.' The most well-known one is by Jeff Noxon, which has been continuously improved by numerous clever people.

What do the experts among you think about this?

http://hal9000.vc-graz.ac.at/3rdfloor/projects/diagnose/Diagnose-Interface.htm

- Should one buy self-made OBD2com modules (e.g., on eBay) without risking damage to their ECU? Or is it better to build one yourself (I'm very lazy and cheap, so does anyone have one for sale at a good price?)
They are simply too expensive for me, especially those from well-known companies.

Problem 2: I want to install an RS4 speedometer in my Audi (it looks better, but it has way too many kilometers on it), and my workshop doesn't want to do it. Another workshop wants to charge me more for the installation than the entire speedometer cost me from Resebeck...

- Once I have obtained the immobilizer code from my workshop (7 digits for VW, 9 digits for Audi), how can I accurately change the odometer reading (mileage)? The Audi has two separate data blocks, and what else...?


It would be great if someone had an idea or even a solution to these questions.
(If it goes into too much detail, please email me privately or send me a private message.)