Accessory Switch &
Dashboard Illumination


The Audi Quattro 20V Home

Problems and Diagnostics

Accessory Switch & Dashboard Illumination

Differential Lock
Seat Heater Switch
Other Dash Switches
Window Switch
Mirror Control Switch
Instrument Cluster
Airbag Removal
Auxiliary Gauges
OEM Radio


The luxury of the power accessories in Audi automobiles come with a price: the switches loose their illumination after a few years. Not a major problem, but irritating nonetheless. Rather than replace a $30+ switch, you can usually fix them with a few dollars in parts and a truckload of patience. A soldering iron is required in most cases, and several tiny (jeweller's) screwdrivers will come in handy.

Differential Lock Diagram Bulbs
(Sean Douglas)
There are three bulbs in the little diagram in front of the diff lock switch. Two of the bulbs are for illumination when the headlights are on, and the third lights up when the diff lock is activated.

  1. It may be possible to remove the diff lock switch and diagram by prying it up from the top, but rather than risk damage, its safer to get at it from the bottom. The hardest part about removing the console is removing the handbrake covers.
  2. Remove the center console as per Bentley. Briefly, remove the two 8 mm bolts under the rear ashtray and the one behind the little plastic cover in front. Remove the handbrake covers by prying the rubber back from underneath and pulling off the plastic cover. The plastic cover is secured by a metal tab in the handbrake lever. Using a small flat screwdriver, slip under rubber cover and gently pry the plastic tab up and pull the handle cover forward. The console can now be lifted up.
  3. Remove all electrical connectors and lift console out.
  4. Remove the diff lock switch and diagram by pressing the rear tab in and pull up and out.
  5. At your work bench, remove the 4 phillips screws to expose the bulbs. There are 3 bulbs in total, 1 for the diff lock light, and 2 for illumination of the axle diagram. They are soldered to a mini circuit board.
  6. Take the switch back to the car and plug in to determine which bulb is the culprit. The lights and ignition have to be on for the bulbs to work. Check the operation of the diff lock light too.
  7. Remove the bulb with your soldering iron and vacuum bulb. You can replace with a Radio Shack bi-pin 12v 50 mA (272-1154), but some have found that to be too bright and hot. A better option would be a similar 25mA bulb that should also be available at Radio Shack. The diff lock light is hard to get at because it's surrounded by a plastic shroud.
  8. While you've got the console out, there is a small bulb for the cigarette lighter (Osram 1.2 w) and one for the rear ashtray. These simply plug in and are available from a dealer.
  9. Installation is the reverse order.

Seat Heater Switch Bulbs
(Ray Calvo)
For some reason, the switch illumination on the seat heaters is always on (unlike the other switches which are illuminated only when the headlights are on). That's probably why the little bulbs inside tend to burn out more frequently on these switches. Here are steps for replacing the bulb, rather than the whole switch:

  1. Remove switch from dash by carefully prying out with a screwdriver on the top and bottom edges alternately. As you pry, the harness on the back of the switch may come loose. If not, just disconnect it once the switch is out. Gently prying off the switch cover, then GENTLY using a pair of needle nose pliers works great. There is not a lot of slack in the wiring harness. Brute force is strongly discouraged.
  2. You will see an outer plastic housing that covers the circuit board, red plastic housing, and rotary dial. This housing can be pried off by inserting thin screwdriver blades under the sides of the switch (should see little prongs sticking into the sides of the housing that have to be pried free). Pull out the housing SLIGHTLY, then lift out the two metal bars at the top and bottom of the switch that act as the catches to hold the switch in the dash. Hold the switch so the side of the dial faces up (circuit board is down), then slide the housing off.
  3. WARNING - BE VERY CAREFUL OF THE ROTARY DIAL. DON'T DISPLACE IT OFF THE RED PLASTIC HOUSING! There is a microscopic (almost) steel ball that acts as the switch detent; if you lift the dial off the red plastic you'll lose it and never find it.
  4. Now, the red plastic/dial unit has to be pried vertically up away from the circuit board. You might be able to pry the legs of the red plastic out of the locating holes in the circuit board, but in my case they broke off (no major problem; the outer black plastic housing will hold everything in place on reassembly). You can also just cut or grind the tabs off of the legs on the other side of the circuit board to avoid the chance of breaking the board.
  5. With the red plastic/dial assembly out of the way, you can unsolder the old bulb and solder in a new one. I recommend the Radio Shack 12V DC, 60mA micro lamps in a 2-pack (Cat. No. 2721092B).
  6. You can check for functionality by hooking a 12v power source across terminals 3 and 5 (see back of switch); bulb should light. MAKE SURE OF CONTACTS if you do this; this is how an anonymous lister fouled up and blew the rheostat. Pin outs: pin 3 = +12v to light bulb, pin 5 = gnd for bulb, pin 6 = +12v to rheostat, pins 2 and 4 are outputs to control unit. Light bulb function is NOT an indication of switch/circuit functionality.
  7. Reassembly is a reversal of removal. Don't forget the little black spring clips. After the switch is all back together, when you try to reinstall it, you'll find there's no way to hold the harness in place to force the switch contacts into the harness. One option is to remove the radio, then hold the back of the harness in place with the short end of an Allen wrench while pushing the switch into place. Alternatively, you can remove an adjacent switch.

Other Dash Switch Bulbs
John Cunningham, Mark Chang, Brent Henry)
The rest of the switches on the dash (besides the seat heater switches above) have a relatively simple design. The bulbs can be replaced by following these general steps:

  1. Remove switch from dash by carefully prying out with a screwdriver on the top and bottom edges alternately. As you pry, the harness on the back of the switch may come loose. If not, just disconnect it once the switch is out. Gently prying off the switch cover, then GENTLY using a pair of needle nose pliers works great. There is not a lot of slack in the wiring harness. Brute force is strongly discouraged.
  2. If the front of the switch was not removed in the above step, pop it off with a small screwdriver.
  3. There will usually be two bulbs--one is the panel illumination light, the other is the 'activated' light for when the accessory is on. The bulb may be soldered in, or plugged in to a socket. If it's a socket-type, you can carefully grab the bulb with needlenose pliers or tweezers and pull them out. It might take a good tug, but the bulbs are amazingly stout, so don't worry too much about crushing them. If it's soldered in, you'll have to desolder the old one and solder in a new one.
  4. Replacement bulbs can probably be found at Radio Shack or possibly an auto parts store. Wagner 17037 Auto Indicator Bulbs are said to fit the sockets nicely, but may be brighter than the originals. Just push the new bulbs into the sockets and put it all back together. For soldered bulbs, the standard Radio Shack 12v - 60mA bulbs should work fine. When you try to reinstall it in the dash, you may find that there's no way to hold the harness in place to force the switch contacts into the harness. One option is to remove the radio, then hold the back of the harness in place with the short end of an Allen wrench while pushing the switch into place. Alternatively, you can remove an adjacent switch.

Window Switch Bulbs

  1. Remove switch assembly from armrest or door panel. This process varies with the door, and is roughly outlined in the relevant Bentley. For front doors, the lower armrest cover is removed by a screw or two, then the now revealed screws removed, the upper panel slid rearward a tad, and then weaseled upward, taking care not to damage the leather. The electrical connector to the switch is removed, and the switch itself removed by applying pressure to the tangs holding it to the panel.
  2. Unlike the seat heater control, or remote mirror control, for example, the window switch base (where the connector pins are) does not have exposed protrusions for locking the base to the cover (the black plastic covering the switch sides). Instead of being exposed through slots in the switch cover they lock into the cover internally, four places. Before trying to release them, an additional step is needed. The actuating lever must be removed. Examine the actuating lever assembly (the part one actuates the switch with). It will be seen to pivot at its center. The lever has two axial protrusions that snap into holes in extension tabs that are part of the switch base. Carefully pry out one side, say right, of the cover at the lever end while pushing the lever to the left. Pull up on the lever. It should come out of one pivot hole. Then it can be pried from the other pivot hole.
  3. Removal of the lever will expose a clear plastic covered area, below which is the light emitting diode (LED) that has failed. It will also expose four extensions of the brown colored switch base. Two are the pivot points described above. Two at the other sides are locating pins and are used to push the base out from the cover. To accomplish this, tools such as jeweler's screwdrivers are used around the base to release the base protrusions from the slots in the side cover. Using your 6 hands, wiggle and push until the base begins to slide out. Then the locating pins can be further pushed until the switch is apart.
  4. Clean the transparent plastic of any plastic chips that resulted from the preceding process. Clean out historical spilled substances from the parts, if applicable.
  5. The LED is a T1 size, and can be replaced by a same size one from Radio Shack (don't have the number handy, but my Radio Shack store had only one type of this size, a package with two LEDs, rated for 10 mA nominal, 20 mA absolute maximum). In the switch I just repaired, the LED was in series with a 270 ohm resistor. This would allow 50 mA to flow with 13.5 volts across the switch. I don't know if this was a fabrication error or Audi uses particularly robust LEDs (evidently not given their propensity to fail), but for the new Radio Shack lamp, a larger resistance is called for. Replace the resistor with a 1 kohm 0.25W resistor, or thereabouts (up to 1500 ohms would be fine).
  6. Replace the LED, taking into account that the long lead is to be positive and goes to switch pin 4 (the center one) whilst the shorter lead goes to the resistor (which ultimately goes to ground after a tortuous path through the switches and control unit). The LED is easily damaged by stress on its leads, so plan and bend before soldering. Use an iron that is not so hot that it smokes the solder rosin. Install the LED so it is in the center of the appropriate switch section. (Check with the cover portion to ensure proper alignment in all three axes.) Make sure the solder flows properly and forms a fillet that is indicative of a noncold solder joint. Check that the two lever extension pieces that slide in the base assembly are still free to move. *** Avoid using the soldering iron tip to reconfigure the plastic parts. ***
  7. This would be a good time to use some CAIG ProGold or DeoxIT on the switch contacts, if available. Given the high currents that flow to the window motor, this is not critical.
  8. As the Bentley says, assembly is the reverse of removal.

Mirror Control Bulbs

  1. Remove the console assembly from the armrest. This process is illustrated in the Bentley. The steps are, briefly: loosen the three screws from the underside of the front section of the armrest. You'll need a 4 or 5mm allen wrench for them, I think. One is just underneath the top edge, the second is located where the armrest angles upward, and the third is at the handle area (the part you grab to close the door) and screws the front piece into the rear section of the armrest. You should now be able to remove the armrest and the window switch/mirror control/seat memory unit just slides out the left side.
  2. Disconnect the electrical connector to the mirror control assembly. No other connectors need be removed if only the mirror control is to be repaired. On the right hand of the underneath of the console assembly is a plastic tang overlapping a protrusion on the mirror control assembly. Pry the tang slightly to the right and release the protrusion slightly. Using a hook of some kind, then pull the spring-loaded tangs on the left of the control assembly. The control assembly should now be free and can be removed through the inch or so gap between the console surface and the armrest. Now you can take the control assembly to a work area where small parts can be kept under control.
  3. The mirror control assembly is constructed in a manner similar to the seat heater switches. That is, there is a plastic shell that overlaps a set of protrusions. Removal is annoying but possible. Start at the spring-loaded tang end and use several tiny screwdrivers (or anything small and thin) to hold the tangs in by placing them under the plastic shell. Then use more jewelers screwdrivers to pry the other areas of the plastic shell to get them up over the protrusions. This is harder than for the seat heater switches as there are 6 protrusions altogether plus the spring-loaded tangs. But success comes to he/she who is patient.
  4. Pull off the plastic shell with the control side down! This will keep two ball bearings under control that are balanced on two posts. Put another way, pull out the circuit board with attached connector pins by pulling up.
  5. Once exposed, the two lamps are obvious. They can be replaced with the usual Radio Shack 12V DC, 60mA micro lamps in a 2-pack (Cat. No. 2721092B). I recommend replacing both bulbs, even if just one is blown. Note that Audi will not likely obtain a NASA quality award for their soldering/circuit board construction. Use a solder sucker on the lamp connections and keep your iron temperature just high enough to melt the solder cleanly without burning the flux. Check the other joints for cold solder connections. Check that the circuit trace did not move and cause a short. Check that the solder did not overrun the narrow circuit trace gaps and cause a short. Clean off the new flux with denatured alcohol and a brush.
  6. If necessary, the control assembly contacts can be cleaned, including those under the rubber pad. Depending on the selection of cleaning solvent, you may or may not improve things.
  7. Reassemble in reverse order, making sure the ball bearings are in their proper location. Once the plastic shell is snapped into the protrusions, you don't want to go in there again. Return to the vehicle and test the control assembly by reconnecting it outside the console. The connector should reach. The ignition key has to be on to run the mirrors. Shield the assembly from ambient light and check that the new lamps work. (Turn on the headlight switch.) If everything checks out, the control assembly can be reinstalled in the console, reconnected, and the console returned to its normal location. Be sure all other electrical connectors are in place. (Turn off the key and the headlights.)
  8. I found reinstalling the console to be tricky, as there was always some part that wanted to obstruct the reassembly. Some weaseling was ultimately successful in getting it back into position.

Instrument Cluster Bulbs
(Ray Calvo)
Since this procedure describes removing the steering wheel, it should only be used on non-airbag cars. Even if you disconnect the battery, the airbag will still be active! I've heard that you can remove the cluster without taking the wheel off, but it's a little tougher. If you're feeling brave, try the airbag removal instructions below.

  1. Disconnect battery ground strap
  2. Pull off horn pad
  3. With wheel in straight ahead position, unbolt wheel and remove. You may want to mark the exact position of the wheel with some white-out or marker before removal.
  4. Remove upper steering column switch cover by using Phillips head screwdriver to remove two screws from the bottom cover. The top cover must be raised slightly, then pulled toward you.
  5. Just behind this cover you'll see two screws at the bottom of the instrument cluster. Remove them.
  6. You can now tilt the cluster to the rear of the car, remove the various plug-in harnesses and remove the cluster.
  7. Bulbs are 1/4 turn screw-in style at the back of the cluster; there are a ton of them!
  8. The parts manual lists the following part numbers:
    Black base bulb: 1.2 W P/N 893 919 040  --  Alternative source: OSRAM P/N 2721MF
    White base bulb: 1.1 W -- Has no P/N, but notes for black base bulb above say that it can be used to replace these
    Green base bulb; 2.0 W P/N 893 919 040A

Airbag Removal
(Brian Ulmer)
This is a dangerous operation. You should first consult the Bentley manual for complete instructions and safety information. (i.e., Don't come running to me if somebody gets maimed or killed.)

  1. Disconnect ground strap on battery.
  2. Disconnect airbag disable connector located behind a small panel in the ceiling of the driver's footwell.
  3. Remove the plastic cover over the top of the steering column by removing two screws from the bottom.
  4. Disconnect the airbag connector on the right side of the now open bottom half of the plastic cover.
  5. Unscrew the two torx screws holding the airbag unit in place. There is one on either side which can be accessed through a little hole on the back of the steering wheel.
  6. Remove air bag unit, undo hinged metal clip covering the airbag wire connection and remove the connector.
  7. Place the airbag somewhere where it won't kill anyone if it decides to go off. Face up is preferable.
  8. Reinstall is the reverse of removal.

Auxiliary Gauges
(Mike Benno)

  1. Remove 3 bolts holding down rear center console (2 back by the rear ash tray, and one under little plastic cap behind shifter)
  2. Remove parking brake grip by inserting flat screwdriver in slit on passenger side of grip. Lift plastic tap over catch pin (hidden), while pulling grip forward.
  3. Remove parking brake sleeve by prying tabs out from underside of lever. Then remove console unit.
    * You can avoid steps 2 and 3 by lifting the handbrake as far as possible, then pulling the rear console up and back as far as it will go on the handbrake lever. Make sure that you don't damage the wires for the diff lock or ashtray light.
  4. Unscrew shift knob, and remove shift boot (optional).
  5. Pry wood pannel from AC control unit, use thin flat object (kithchen knife). Remove two screws at bottom of space holding a plastic retaining bracket for the gauges.
  6. Pull gauge console forward to gain access to back of gauges. You can now see the bulb sockets plugged into the gauges.
  7. Remove and replace bulbs. P/N for bulbs is N 017 751 2 (12V, 1.2W).

OEM Radio Illumination Bulbs
(Ray Calvo)

  1. Remove the radio from the dash. A special tool is used in the holes on the left and right of the faceplate. You can ask any audi shop to take it out for you, or you can just cut a wire coat hanger in half and make two u-shaped pieces. Insert the pieces into the four holes and pull the unit out by grabbing it through the cassette door.
  2. Once the radio is out (remember to deprogram it, or make sure you have the the radio code, depending on the vintage of the Wiesbaden unit you have.), pull of the volume/balance knobs and the bass/treble knobs.
  3. Unscrew the brackets at each end of the radio.
  4. Remove the nosepiece. The nosepiece is held on with 4 clips -- 2 on each side and 1 on the top and 1 on the bottom. The clips are accessible from the outside of the unit. Using a small screwdriver, gently press the clip in and pull the nosepiece out at the same time. The clips on the top and bottom are offset from the center.
  5. With the nosepiece off, you should see the screws that hold the LCD display to the metal case; unscrew them and you should see the little bulb behind it. It's got a little orange rubber on it, which you take off an put on the new bulb.
  6. The biggest problem is the length of the wires running to the bulb; there is not much slack. Cut off the wires as close to the bulb as possible.
  7. Radio Shack bulb cat. # 272-1154 will work, or possibly cat. # 272-1092B.
  8. Screw the faceplate back on and clip the nosepiece back in place. CAUTION - don't pinch any of the wires going to the bulb; the nosepiece can easily do this and possibly cause a short.

The original driver's key came with an integrated light, which has surely gone out by now.
The battery can be replaced by an Eveready EPX625, Duracell PX625A-1, Varta 625, Radio Shack 23-1504, or equivalent.
The bulb is 1.5V, 0.09A.

See also: Window and Sunroof Problems, Seat Heater Diagnostics, Audio Upgrades

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