|Tech Article Title
|Restoring Temperature Display After Heated Mirror Fix
If you rewire your heated mirrors to use the
defroster switch you may
lose the temperature/gear selector display. Here's a fix I made for my
97 A4. This may or may not work for you and you are performing this at
your own risk. I assume no responsibility if this doesn't work for you.
(Sorry for the lawyer speak but you know how it is)
1) Soldering iron/solder
2) Volt meter
3) Philips screw driver
4) 8mm socket
5) T-25 torx driver
6) Electrical isolation tape
7) Some thin cable
You can do this before or after you've made the change described in the
Heated Mirrors (Wiring to Rear Defrost Switch) article.
If you're not sure if you'll have this problem, just pull fuse #9 and
switch the ignition on. The gear selector/temperature display should not
be visible. If so continue reading.
First, you need to remove the instrument cluster. I followed the
instructions here. One word of
caution. The plastic cover on top of the steering column is painted. You
can scratch it trying to remove the cluster (ask me how I know). To be
safe, cover this area with a towel or something else first. Also, the
left and right side connectors are a little tricky to remove. I used a
screwdriver between the the connector and instrument panel and slowly
rotated it. Once the connector is loosened, it removes easily.
After the cluster is removed we need to verify the wires we'll cut. You
should have disconnected three major connectors from the instrument
panel (I also had two smaller connectors). The ones we're interested in
are the black middle connector that powers the temperature/gear selector
display and the blue connector from the right side of the instrument
Get out your DVM and set it so it can display at least 12v. Grab the
middle connector and
hold it facing towards you so that the wires are on the right and insert
a small straightened paper clip into the last hole on the top row. Turn
on your ignition and measure between the paper clip and ground. You
should measure a little over 12v. Turn off the ignition, pull the #9
fuse and repeat the measurement. You should measure no voltage meaning
we have the wire that's connected to heated mirror circuit. Turn off the
ignition. If you look at the bottom of the connector where the wires
come out, you should be able to tell what actual wire this is. On my car
it was a black wire with a red stripe. Replace the #9 fuse.
Now, grab the connector that
was connected to the right side of the instrument panel. Hold it so that
the wires are to the right. Stick your straightened paper clip into the
fifth hole from the right side of the bottom row. Turn on the ignition
and measure between the paper clip and ground. You should measure about
12v. Turn off the ignition, pull the #9 fuse and repeat the measurement.
This time you should still measure 12v meaning we've found an alternate
power source for our gear selector/temperature display. Turn off the
ignition and replace the #9 fuse. Looking in the bottom of the connector
you should be able to tell what wire connects to this pin. On my car it
was again a black wire with a red stripe.
What we're going to do now is cut the 12v wire from the black middle
connector and splice it to the 12v wire on the blue right side
First, get out your wire cutter and remove some of the black tape that
covers the bundle of wires leading to the center connector. Trim it back
so you have 4-5 cm of wire visible. Now cut the black wire with the red
stripe leaving about 4-5cm of wire to the connector. Strip off some of
Now take the blue connector and burn off some of the insulation on the
12v wire (black with red stripe) you found above. Don't cut this wire!
Also, be careful not to remove any insulation from any other wires. I
burned off about 1cm or so.
Cut a length of wire to span the distance between the two connectors. I
cut a length so that I could lay the wire next to the bundle that runs
between the two connectors. Solder the wire between the cut wire on the
middle connector and wire with the burned insulation. Wrap some
insulator tape around the two exposed ends.
Now carefully, lay the instrument panel on the top of the steering
column cover. Reconnect all connectors. Turn on the ignition. The
temperature/gear selector display should come on. Turn off the ignition
and pull the #9 fuse. Turn it on again and the temperature/gear selector
display should still work.
Tidy up the jumper wire by fastening it to the middle connector bundle
with some insulator tape. Put the instrument panel back it and proceed
to rewire your heated mirrors. Now you'll have the best of both worlds!