So, when I got my car (’96 Audi A4 B5) the remote control for the central locking didn’t work. We replaced the batteries and did a series of tests to try sort it out but nothing worked.

We took it in to the local Audi dealership who after a morning of having it returned it to us with a quote for R8000 (excl). We said thank you and I have used the key ever since.

It seems that something went wrong with the Infra-Red system my Audi used (I know from 1997 they switched to RF remotes) and the previous owner never bothered to fix it.

If your Audi came out before the IR remotes, this approach should still work, if it came out after the RF remotes, check here.

Now the Audi’s whole security system, the alarm, the pump for the central locking etc are all contained in one neat little box located in the boot under some panels. So although 90% of my box still worked (everything except the infrared circuitry) they would have to replace hte entire unit. Thus the huge cost. I’ve seen 2nd hand units advertised for about R3000, so it is just an expensive component.

So recently I got thinking, couldn’t we just try and install a conventional wireless system around the current system.

Because the infrared system was stuffed, we decided to go at it a different way, and use the signal that gets sent to the alarm system when you manually unlock the driver’s door.

This invloved taking the panelling off and finding the wires that go from the lock to the alarm system. 3 wires were found, a brown one (we think it’s some form of check to see if the door is open or closed) and the two important ones, a red & brown cable witch is shorted with the car’s earth when the key is used to lock the car, and a grey & white cable for unlocking.

To get at the security box in the car open the boot and remove the mats covering the side wall and bottom area off to the right of the boot. I had to remove a little storage box by just lifting it up and unclipping it. There are also two plastic caps which keep the mat in place, remove those, then you just need to use a bit of force to work the carpet out from behind the plastic fascia. You shouldn’t have to unscrew anything.

Once removed you should see a foam box to the right, lift the cover and a plastic box should be lying there. There are 3 wiring harnesses, the two outer ones can be pulled straight out, but the middle (power) one needs a screwdriver or something to unclip. There is also the air pipe which can just be pulled off. You can then quite easily remove the security box. This is just to make soldering easier.

Of the two outer plugs, one is smaller than the other. This is the one that takes signals from the lock in the driver’s door. You will find two wires that correspond to the two we found in the driver’s door. The grey & white and red & brown ones.

And voilà!

Connect these onto a remote control receiver and you’ve got yourself a new remote control.

Power for your receiver can be taken from the middle wiring harness. Check your polarity with a multimeter, but for me the brown cable was earth (which I used as the earth for the lock and unlock signal as well) and the red one next to it was positive. This gives you the necessary 12V.

I haven’t connected my remote control yet, as I’ve had to shop around for a decent one at a cheap price. I eventually found this on ebay for R240. At a local security shop they sold a 3 channel receiver (for garage doors) for R310 and a remote with two buttons is R150 rand. Those are code hopping ones, which are more secure than the ones I bought, and will work fine in a car.

note: When you use the key, turning it once turns off the alarm, and physically unlocks your door. That means that if you push your remote control once, it will turn off the alarm and NOT unlcok your front door. If you turn the key twice in succession it unlocks all the doors. Likewise, pushing the remote’s button twice will unlock all the doors.

If someone manages to hack the infrared section of the circuitry, you would not have this problem. I may get round to looking through it one day, but at the moment this works :)

When I get my remotes I will see if I can build a small circuit to send two signals instead of one, so I don’t have to push twice each time.

I have already soldered all the wires in place that I need to install my receiver, and have checked that they work by shorting them. I will repost once I have received my package and installed it.