Damn..haven't been to Audiworld in a few years...here's the right up ya'll. Hope this helps.
Section 1: Parts needed for 1993-1995 Audi 90 quattro (not sure if this procedure works for 88-92 or FWD's or cabriolets).
a) trip computer/ autocheck module from a 1988-1992 Audi 80 (quattro) or 90 (quattro) or a 1990-1991 Audi coupe quattro.
a trip computer from a 200 will *probably* not work.
b) switch for the trip computer. Early b3's will use a switch in the center console by the heated seat/defrost switches, which is the easiest to install. The other option is the later b3/coupe quattro/b4 style at the end of the wiper stalk. If you have a mid to late '95 with the newer style airbag wheel, you'll probably need a '96 to early '98 a4/a8 stalk assembly.
c) wiring pigtails from the donor car. The trip computer is a 10-pin black connector, the connector for the console-style switch is blue (I haven't tried the wiper stalk, so I do not know what color that connector is), if you plan to install the autocheck system too, the autocheck is a 26-pin white connector. Both the trip computer and autocheck plugs are connected to the autocheck/trip computer assembly.
d) Proper coding card for you car. (See "Installing the trip computer module" <--- Ryan always ephasized the importance of this, but mine was not what he recommended but what originally came with my b4 90 and it worked fine.
[Picture of the blue connector shows 5 wires...from top right to bottom left = top is a blue wire, second row l>r is black then brown, 3rd row l>r grey then green.]
Section 2: Making the wiring harness
1) First remove the old taping material from both the trip computer and switch conectors.
2) Install splice connectors to all 5 wires on the switch connector (blue). They will match up exactly with the wiring harness for the trip computer (black). Wires = blue, black, brown, grey, green.
3) Tape all 5 wires together as tight as possible to help snake them behind the dash. You will only need one other wire out of the trip computer connector (black connector) which is the yellow wire. This wire is referred to as teh "consumption wire". I spliced in a piece of black wire to the yellow wire in the computer pigtail. The rest of the wires are not used on a 93-95 90 quattro and were taped off.
Section 3: Installing the wiring harness
1) First choose/find a blank location in your center console. Remove it by prying gently at the bottom of the blank with a small flat-head screwdriver. Also, remove your instrument cluster and the knee-guard panel above the pedals.
2) Fish the wiring harness from the switch location to behind the instrument cluster.
3) Now that you have the wiring harness installed, connect it to your switch and pop it into the center console. Only thing left with the wiring is to connect the yellow wire. For this you need to get up into the relay panel which is behind/above the panel above the pedals. To the right of the relay/fuses you will see a few differently colored wiring connectors, and we want to use the black one closest to the floor of the car. In my car there were 2 yellow wires, one going all the way through the back/front of the connector, and one only in the back of the connector. I chose to use the one which wans't connected to anything. You will basically want to tap this wire.
Section 4: Installing the trip computer module.
1) Remove the midicheck module from the back of the cluster (the big white thing) This is pretty simple once you have the cluster out. Ther eare three screws (one to the left of the 4 bulbs, one on the opposite side, and one below the white harness connector.) Once they're removed, simply pull the module out of the cluster.
2) Install the trip computer/autocheck module into your cluster. This unit uses 4 screws.
(In the picture, it shows a little fuel range calibration wire/circuit board installed behind the gas guage .. if you have the autocheck mod..you'll know what i'm talking about. This will need calibration, so don't "pop" it in just yet. )
3) Install the proper coding card. If you got your cluster from a 1990-1991 coupe quattro, you should be fine. However, if you got your cluster from a 1988-1992 80/90, the coding card will not be correct for your car. Some have modified the 80/90 cards to work in their 1993-1995 90 quattros, I however purchased the proper card.
1988-1992 audi 80/90 quattro 10v/20v coding plug = 5436893919 vdo 100 G
1990-1991 audi coupe quattro (7a) and 1993-1995 audi 90 quattro coding plug = 5869895919 vdo 100 P
* Note: FWD coding cards are different part numbers than quattro models.
Section 5: Calibrating the trip computer
The last step is necessary so that the trip computer knows how much gas is in the tank. You need a full tank of gas to properly complete calibration.
What you want to do is reinstall the instrument cluster back into the car, but leave the little fuel range calibration wire/pcb board dangling out where you can adjust it with a very small flat-head screwdriver.
1) With the ignition key in the OFF position, press and hold down the trip computer RESET button.
2) Keeping the RESET button pressed, turn the ignition key ON. Verify that the correct trip computer code is displayed (a532 for the coupe quattro and 1993-1995 90 quattro)
3) Release the RESET button and verify that the next number displayed is approx. the amount of fuel in the tank. This is displayed in liters x 10. The reading will probably be higher than what is needed for a 93-95 90 quattro, but with a full tank of gas, this should be somewhere between 579 and 610. *Note: Even though MPG is displayed in gallons, it's calibrated in liters.
4) You will now calibrate the reading on the range calibration board. The lowest I could get my card to go was about 579 (57.9 liters), which is just below the maximum capacity of 610 (61 liters). From the factory, these cars are set with a 5 liter/1 gallon reserve. To adjust the switch, turn it to the left very very slowly and watch the trip computer display. It will slowly go down. Note: Just remember, the maximum capacity of a 93-95 90 is 61 liters (610 on the trip computer), so anything above that is extremely innacurate.
5) Now turn off the car, pop the range calibration board in behind the gas guage (only has one orientation which will work - pay attention to how this was on the donor cluster if possible)
Verify all your conenctions and then reinstall the cluster in the car.
YOURE DONE. (WITH TRIP COMPUTER)
If everything works correctly, you should get the following functions:
-Instantaneous fuel consumption
-Miles or KM to empty
-Fuel consumption per trip
-Driving time (max range 23 hours, 59 minutes)
-Average fuel consumption
-Average driving speed
The RESET touch control in the center of the switch serves several functions.
By depressing reset for 2 seconds, the "fuel consumption per trip", "driving time", "avg. fuel consumption", and "avg. driving speed" can be reset.
The instant fuel or miles to empty cannot be reset.
Section 6: Autocheck Parts
Audi parts required
-autocheck (with or without a trip computer) module form a 1988-1992 audi 80 quattro/90 quattro or a 1990-1991 audi coupe quattro.
-wiring pigtail from the donor car (the autocheck is a 26-pin white connector, thr trip computer is a 10-pin black connector. Both the trip copmuter pulgs and autocheck pulgs are connected to the autocheck/trip computer assembly.
Section 7: Autocheck wiring background
On the autocheck pigtail (white connector) there are 8 wires.
1) brown with black tripe (RPM signal from ECU - excepts '88 80 4 cyl.)
2) grey (to front/rear bulb monitors)
3) green with blue stripe (RPM signal from ECU)
4) blue with black stripe (.3 bar oil pressure switch)
5) brown with green stripe (RPM signal from ECU - '88 5-cyl. only)
6) Red (to rear bulb monitor)
7) Brown with red stripe (windshield washer level)
8) White with grey stripe (1.8 bar oil pressure switch)
This installation information is to thet the autocheck to work with the exception of the bulb monitors. This can be done, but I didn't as I find it kind of uneccesary. I didn't do it also because I use Euro/HID which renders this feature useless anyway.
You will still get warnings for:
-brake fluid level low
-coolant level in expansion tank too low
-coolant temp too high
-engine oil pressure too low
-battery/charging system defaults
-low gas warning
You will not get (with this right up):
-brake light out
-washer fluid low
Section 8: Autocheck installation
1) First off, you will need to remove instrument cluster and install the autocheck unit. If you have a trip computer/autocheck, or even just an autocheck module, this will be the same as Section 4: Installing the trip computer module.
2) Locate your OLD minicheck module plug (white, 14-pin connector usually bundled with the yellow instrument cluster connector). You will want to install wire taps on the following wires;
a)Green with blue stripe (RPM signal from ECU)
b)Blue with black stripe (.3 bar oil pressure switch)
c)White with grey stripe (1.8 bar oil pressure switch)
Connect the wire-taps to the white 26-pin autocheck pigtail you have (wire colors are the same).
3) In addition to this you will want to tap a brown (ground) wire from either the yellow (closer) or blue (other side of the cluster) instrument cluster connectors already existing in your 90. Run a short piece of wire out of the tap so that you can ground the following wires:
a) grey (to front/rear bulb monitor)
b) red (to rear bulb monitor)
If our windshield washer fluid level is going off after installation, ground it here too. This basically "fools" the autocheck to thinking those functions are operating normally, otherwise every time you start the car, it will yell at you for bulbs being out.
4) The rest of the wires you can tape off, as they aren't applical on the 1993-1995 90 quattro.
5) Verify all of your connections, and reinstall the cluster.
Now start the car. If everything is working properly, you should get the normal "OK" symbol. You can also press the left most peg (cluster lighting dimmer) on the instrument cluster in to have it "check" all the functions. On top of the "fooled" functions, mine also shows the symbol for "brake pad wear", yet..no 1988-1992 80/90s that i know of ever had this function.