First off, I accept no responsibility if you mess up anything in your car! I am just sharing with the world how I was able to get this to work. After all of the time I spent researching this, I felt it was necessary to document it somewhere where others could benefit from it. I also only discovered how to get this to work on an FIS cluster. It is probably possible on an MFA or standard cluster but I have no idea what else is needed so do not ask me any questions unless you are using an FIS cluster!
Now, on to the specifics…
With the help of Graeme, I was able to install the Audi bulb monitoring system in my Jetta. With the addition of a relay module under the dash, the car monitors the headlights, tail lights and brake lights. If one of them goes out, one of two messages will pop up on the FIS display. The first says “Lights Failure.” This comes on if one of the headlights or one of the taillights goes out.
The second says “Brake light Failure” and will show up if (obviously) one of your three brake lights goes out.
The warnings do not show up until the respective system is energized (you turn on the light switch or press the brake pedal).
I don’t even know how many times I’ve been pulled over for a burnt out light and for some reason it seems all MKIV’s are plagued by having their bulbs die regularly. Since I already had most of the necessary components, this mod only cost me about $50 for the relay and relay socket. There are quite a few other necessities as well though.
Stuff you need:
Lampcheck relay: 4B0 919 471 A
Relay Socket: 4A0 937 529
Repair Wires: (each repair wire has 2 connectors on it)
000 979 212 x2 (extra-large female connector)
000 979 227 x4 (large female connector)
000 979 225 x6 (medium female connector)
000 979 133 x1 (for cluster terminals)
An Immobilizer 3 MKIV FIS cluster (mine is p/n 1J5 920 946 A)
A surface mount 3 diode array. I used this one:
Vagdashcom or VagTacho (for modifying the cluster’s EEPROM)
Lots of #18, #16, and #14 wire
So the basic concept is that you have to intercept the circuit going to each bulb and pass it through the relay. There is a resistor that each light passes through in the relay which has a resistance that is close enough to zero that is almost negligible. The relay can detect if there is current across that resistance and determine if the bulb is out or not. Here is a simple explanation…
Light switch->Fuse->Light Bulb
All you have to do is insert the relay between the fuse and light bulbs:
Light switch->Fuse->Relay->Light Bulb
Most of the information on the wiring aspect can be found in this thread on tdiclub:
Sounds simple enough right?
The easy part is doing all of the wiring through this relay. Once it determines what is going on with your light bulbs it sends a signal to the cluster to tell it if there is a problem. The issue with that is… (as far as I know at least), no MKIV cluster comes equipped with the internal circuitry to connect this signal to the cluster’s internal microprocessor. If you enable the warnings in the cluster’s EEPROM, they will show up indefinitely and you will not be able to cancel them or get them to go away… which is where the for mentioned diode array comes in, and probably where most people will give up. I have to admit, opening up a $400 FIS cluster to solder components to the board was terrifying for me, but I decided to give it a go anyways .
Modifying the cluster:
1. Remove and disassemble your FIS cluster. Once the internal circuit board is removed, locate this area on the board located near the blue plug. The black rectangle circled on the left of the picture is what you have to add (if it is not empty, you are very lucky and do not need to do anything to the cluster! You may skip to step 3).
2. Solder the diode array onto the board. You have to solder it in so that the diodes are all pointing down with respect to the picture. The dot on the chip gives you a frame of reference. This is the missing connection to the microcontroller I mentioned earlier. It basically prevents any voltage from entering the microcontroller and damaging it.
3. Reassemble the cluster and install it back into your vehicle. Now get out the laptop and Vagdashcom or VagTacho!
4. Modify the following addresses in your cluster’s EEPROM:
Change the value at address 1E9 to A9
Change the value at address 1F7 to 35
5. Open up Vag-com and go to instruments and then coding.
6. Add an 8 to the first two numbers of the coding. (07xxx becomes 15xxx).
7. You are now done with the laptop and all of the coding! If you turn the vehicle on, both warning lights should show up.
8. To test if you soldered the diode in correctly, ground pins 6 and 19 on the blue cluster connector. This should cancel both of the warnings. If not, you did not solder the diode in correctly.
Wiring in the relay:
This is the most time consuming part and if you want to do it later as I did, you can ground both pins on the cluster’s blue connector or remove the 8 you added to the cluster’s soft coding. There are 17 wires that you have to connect from the relay. You have to run wires to the cluster, the fuse box, the rear taillights, and two connectors that are located inside of the wiring harness directly behind the hood release lever. You have to actually unwrap part of the body harness to locate them. Just feel around on the harness behind the hood release lever and you will be able to tell where they are. Here is a picture of where they are located:
There are two connectors in this picture, a beige one and a black on in the top that is kind of hard to see. I forgot which one is which but I have the wire colors that you need to tap into.
There will be a bunch of empty spaces in the relay plate underneath the dash. Just put the new relay into any two spots that makes the wiring easiest (it is a double relay so it takes up two spots).
Here is the list… I included the wire sizes based off of the Bentley manual for the Audi TT and the lengths that I approximated when making my harness at my desk. The lengths were all long enough to reach to the respective areas. The list explains where to connect the wire from the lamp check relay. I made a harness at my desk beforehand to simplify things:
Pin 1 – #18, 3’ – Tap into black/blue wire on fuse 5 in fuse box in the driver’s side door.
Pin 2 – #18, 3’ – Connect to ground.
Pin 3 – #18, 5’ – Connect to pin 19 of cluster’s blue connector (brake lights ok signal).
Pin 4 – #16, 20’ – Run a new wire to the rear right brake light and replace the existing red/black wire in pin 4.
Pin 5 – #16, 6’ – Input for the brake lights, located behind hood release. Cut the incoming red/black wire and butt splice your new wire to it.
Pin 6 – No connection
Pin 7 – #16, 1’ – Tap into pin 5
Pin 8 – #16, 15’ – Run a new wire to the rear left brake light and replace the existing red/black wire in pin 4.
Pin 9 – #18, 5’ – Connect to pin 6 of cluster’s blue connector (headlights and taillights).
Pin 10 – #16, 6’ – Input for right rear tail light, located behind hood release. Cut the incoming grey/red wire and butt splice your new wire to it.
Pin 11 – #14, 3’ – Input for left low beam, remove yellow/black wire from fuse 21 in fuse box and connect the new wire instead.
Pin 12 – #16, 6’ – Output to right rear taillight, located behind hood release. Butt splice to the outgoing side of the grey/red wire that was cut in the pin 10 step.
Pin 13 – #14, 3’ – Output to left low beam, cut the yellow/black wire that was removed in the pin 11 step and butt splice to your new wire.
Pin 14 – #14, 3’ – Input to right low beam, remove yellow wire from fuse 20 in fuse box and connect the new wire instead.
Pin 15 – #14, 3’ – Output to right low beam, cut the yellow wire that was removed in the pin 14 step and butt splice to your new wire.
Pin 16 – #16, 20’ – Run a new wire to the third brake light and replace the existing red/green wire in pin 2.
Pin 17 – #16, 6’ – Output to left rear taillight, located behind hood release. Butt splice to the outgoing side of the grey/black wire that is cut in the pin 18 step.
Pin 18 – #16, 6’ – Input for left rear taillight, located behind hood release. Cut the incoming grey/black wire and butt splice your new wire to it.
Once you are finished, turn the car on and neither of the warnings should appear. Test the functionality by unplugging a taillight or one of the headlights. Once you energize the disconnected circuit (turn the lights on or press the brake) it should give you a warning message on the FIS screen indicating which bulbs have failed.
The bad thing about this mod is that you won’t really get anything out of it until one of your lights burns out. I am still eagerly awaiting that to happen.
Here's a video for proof. I took it on my old cellphone so it looks like crap but you get the idea: