Window Switch Lamp Repair for Archives - Long

[KSMITH1@mailgw.sanders.lockheed.com]

To supplement the control and radio lamp repair information I and 
others have provided to the list, I detail below a repair procedure 
for the indicator lamps embedded in the power window switches.  It 
strictly applies to the 1988 90q, but is likely to apply to a range 
of Audis due to common use of the switch assembly.

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 one's 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 T-1 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 a 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 non-cold 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 Pro-Gold 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, reassemble in reverse order.

I found the repaired switch using the Radio Shack LED to be 
indistinguishable from the other switches in color and 
intensity.