Just my 2 cents:
I've been having some poor aftermarket fobs that fall apart after two years, so again I bought one of those but now they look more confident in hands:
LINK HERE (ebay)
So, to help You people wire that I will try to explain what I did. The car is A4 B5 12/1998, has central locking and dimmer light pack (I hope that is enough for this topic)
I found best location for wiring is under fuse panel A-pillar, and location for device itself above fuse panel. So You must remove fuse panel, A pillar cover under hood opening handle and cover under steering wheel where you should have relays, power (+12V) and ground connected.
2. Wiring diagram
O.K., at A-pillar, we will mark first connector in first row as POS-A (kinda orange/brown - for central locking pump), and first connector in third row as POS-B (purple/brown - for flash light).
So from the keyless entry users guide to wire checking I went into negative trigger, so the wiring should look like this (wire colours may differ due to year of production):
SPY unit ---> AUDI A-pillar
orange ---> cut
white ---> POS-A brown (lock signal)
yellow ---> POS-A yellow/blue (lock ground)
orange/black ---> cut
white/black ---> POS-A red/brown (lock signal)
yellow/black ---> POS-A yellow/blue (lock ground same as third)
black ---> ground connector screw above connectors panel
red/black ---> *trunk opening (+12v) explained later
red ---> find constant + at relay panel (+12V DC)
small red ---> **not used (power window trigger (-))
brown ---> POS-B black/green (flash lights one side)
brown ---> POS-B black/white (flash lights other side)
* I used trunk opening (A4 B5 don't have that like mercedes-benz boot flipping up) for putting 12V+ to horn (like a panic button). So what I did is took horn relay (it's black #204) and connected wire to bottom horizontal leg of relay and put it back to place. Take a tester/instrument and check, don't blow your relay. In my case connecting most top and most buttom slot for relay powered the horn. Find mass and there you go.
** I never connected power-windows, and that is the thing I will try to find out here and update guide...
So. Take fuses out from SPY cables before You start to work with wires.
4. After soldering and securing wires (do the job as it's supposed to be, I saw few cars here at fire from bad wiring) try to decide, and test things step by step, i did it this way (just follow SPY wiring for correct fuse location):
a) plug main fuse (15A) and test with fob (lock-unlock), You should hear some clicks from device. If You don't check main power and ground wiring
b) plug flash lights fuse and test: lock (gleam once) unlock (gleam twice), turn key to ignition position and test left-right flash light. If you have left and right both powered You have short connected brown wires from Spy device, or You do not have Spy device with two separate wires for flash lights and You need relays
c) plug lock/unlock fuse, go into car or have a key in your pocket (in case something goes wrong), test locking and unlocking. There is possibility that it will not work from first touch as supposed to (maybe only lock or unlock). Try to sync existing central locking with keyless one (for example lock with button inside car/with key and press lock on fob). After that should do fine. I noticed some desync when You use Your key in door lock to do comfort lock (lift windows), but the car is unlocked before by fob. After mounting keyless device, try not to use key in lock.
d) connect trunk (in our case horn) fuse. Lock the car with the fob. Press and hold trunk button on fob. Flash lights sould do triple gleam and horn should be activated for some second.
As we don't have appropriate boot for opening, only function that I had in mind was horn or using this button as panic buttor, or even looking for car at big parking lot in case You forgot where it is/cannot see flash lights on (must be really drunk)
* all other fuses exept main are 10A (red ones), don't mind mine 20A on picture, one felt in sewage drain where I was working and I did not have spare
Yeah, R'n'R job done. But there is one more thing... fobs, flipping key:
What I did...
a) took spare key nice precise pliers and knife and start to split the plastic of a key. When You do that, cut metal part of a key out of a key holder (TRY NOT TO DAMAGE GLASS PART IN KEY). You can leave plastic in middle of a key. VERY VERY Carefuly step-by-step cut glass part out of a key. This glass part is very important, as it is immobiliser passive rfid (coded key).
b) take key blank out of one fob, find some fine metal rasp in local store. Find out if one of the neighbours had some grinding machine for metal. Do the rough part of fitting key to key blank (to fit in fob) on grinding machine, and rest do by rasp, nice and easy.
c) take fob and unscrew three screws at the back, take the plate out. At the place where diode was, turn that hole away from You (you should be looking at open part of fob), take glass part You took from key and put it at left side inside covered part where diode should go. Test that it has enoug cleareance for diode to pass, plate and cover to fit - take one of thoose glues that dry in second (year right ) and make that glass part stay in place. Do it twice just to make sure. That is really important - on my last fobs (I mentioned it) it felt inside fob and I could not start the car, 100 km from home. I needed to brake that first fob, take glass part out and manually put it as near as possible to lock to start the car.
Do not be afraid of damaging the key. BE AFRAID OF DAMAGING RFID (GLASS PART), as you'll make your key useless (O.K. maybe for entering a car).
If You're not sure, take the key to some locksmith that had good reputation and equipment. They can make You new key blank, and even clone RFID part of a key, and You can keep originals as spare keys. But that will probbably cost You as Your keyless entry device
That's it. I hope I helped someone.
For me, thoose aftermarket solutions are better looking, have tripple more range, and have some more options that original from AUDI.
I know cause I was testing (I have keyless compatible pump inside car) original fobs.
Pictures should follow in second post