Here's a simple way to install a GReddy TT in a B5; S4 or A4: 

It should take less than an hour if you don't dick around. Disconnect the (-) terminal of your battery to avoid any fireworks. 

1) Drop the driver's side knee bolster. No need to pull the instrument cluster or anything else... believe it.

2) Remove the bolts that hold the fuse box to that metal bracket - pull it down & pop open the back cover. If you snip that black zip tie at the base of the fuse box (holds the wires in a bundle), it makes picking through the wires a lot easier. 

Find the tiny BLACKw/BLUE wire coming out the back of position #6 - cut it... yeah - CUT IT. 

3) Look up to the left of the steering column. There are two harnesses encased in black nylon webbing. The one closest to you is the one you need. 

Slit it open w/ a razor blade. You need the big BLACK wire, one of the two RED wires, & the tiny REDw/BLACK wire. 

Using appropriately sized T-taps, tap into each of these three & crimp down until you hear the 'click'. Note - use real T-taps, NOT those cheesy "piggie-back" wire clamps. Also: don't believe the hype - solder is pointless if you use T's. 

4) That's it as far as 'finding' target wires - now pop work the trim off around your cupholder using a small flathead screwdriver. Be gentle & don't chip the wood... or whatever you have. 

There are two metal clips that hold the cupholder assembly in place - pry 'em off & slide out the whole crazy-ass assembly & marvel at it's complexity. 

Do the same w/ the fog light / ESP switch assembly - remove the clips & pull it all out. 

5) Now, you should be able to fish the GReddy harness from the cupholder locale to under the steering column. No need to run the supplied two-wire harness - you won't need it... just the big one w/ the RED, GREEN, BLUE, & BLACK (ground). Now you have the harness in place. Plug in the TT. 

6) Wrap the TT a few times w/ friction tape - or electrical tape - & push it into the cupholder recess. It should fit nice'n'snug. Reinstall the trim piece. Looks good, huh? 

7) Back under the dash, cut off the molex plug on the TT harness. You'll have three wires - RED, GREEN, & BLUE. Cut away the BLUE one as far into the TT loom as possible, so as not to leave an exposed end. 

Now you have two wires - RED & GREEN. Crimp on the appropriate insulated male spade connecters to correspond w/ the T-taps you crimped on the BLACK & RED wires in the Audi harness. 

The TT's GREEN goes to Audi's BLACK & the TT's RED goes to Audi's RED. Remember that unused two-wire harness from the TT? Swipe a 10" piece of scrap wire & run it from the tiny REDw/BLACK @ the column to the CAR-SIDE of that tiny BLACKw/BLUE behind the fuse box. 

Use a crimp-cap connecter on the FUSE-SIDE of that wire if you wanna' be nice - otherwise, just pull the 5amp fuse & render it dead. 

8) Find a nice place to ground the TT using the pre-terminated BLACK wire. 

9) Re-connect (-) battery terminal & make sure everthing is powered up & the TT is singing it's stupid little song. Hate it - it's OK. 

10) Clean up your wiring w/ a few zip ties &/or friction tape, put everything back together, & set-up the TT as per directions... inlcuding the dismissal of that stupid electronic jingle. 

Update 

In some instances, the proper "key off" target wire @ the column will be a small-gauge RED-only wire, not the red w/ blk as stated above. The only way to tell what is correct for your particular installation is to T-tap both & simply try each.

If the red w/ blk is wrong, your windows will not work & the TT will turn off when the key is removed. Don't panic! Sit up & crack a fresh beer - you'll need it while you're cleaning up... which will be in just a few short minutes. Now, simply pull the wire from that tap & insert into the other - the red one. That's it - simple.

You'll have two tapped small-gauge wires, but you'll only be using one of them. No worries. Just leave the other tap in place. It's not hurting anything.

It shouldn't take any more than one extra minute to get over this little issue. Sorry for any potential confusion or frustration. Enjoy.

Simple. Good luck. Enjoy.
-Chad (+pressure)