So there are a few of us that have 5-speed swapped our rides. And as awesome as that is (and it's pretty fricking awesome, mind you), there still are a few things left as loose ends. Namely the lack of working cruise control. While there are those of us who do not use, do not need, or do not care about the cruise, these are luxury cars and that is one of the many amenities. Also I have a seriously long drive to work and this was getting pretty annoying.
Note: There is also the issue of no reverse lights. While I may cover that at some point in the future, this DIY is aimed squarely at the Cruise Control Situation, or CCS, as I like to call it.
Note 2: This entire DIY applies to DBW (Drive-By-Wire) cars only (2000+). So ATW and AWM for the 1.8T's and ATQ for the V6 guys.
Explanation of the problem. The reason that the cruise control does not activate is because there is no clutch switch input. Once the ECU is recoded to manual, it expects to see this input as safety for using cruise control with a manual trans. Because our cars have an automatic harness, there is no provision for plugging in the clutch switch. I figured it was just a matter of finding the wire and connecting into it, but in fact the wire does not exist at all in the automatic harness. It is simply not there, all the way back to the ECU. So we must add it.
I have separated this into 2 parts or "phases" if you will. Phase 1 is adding the input wire at the ECU. Phase 2 will be adding the clutch switch and wiring it up at the pedals. The phases are really meaningless. Are you really going to *just* do phase 1? I think not. However it does serve to make my DIY seem more planned out, and somewhat less "thrown together".
*First thing when doing electrical work is to disconnect the battery. Just disconnect the negative terminal at the battery and swing it aside.
Pop off the plastic covering the battery tray and brake booster. This will reveal the ECU plenum chamber (ie: the plastic box).
You will need to remove the five 8mm hex head screws that hold on the top cover. The back 2 are little tricky to get at without removing the wiper arms and rain tray, but it can be done. I have elected to never put those ones back in. Now the cover is off and you can see your ECU. Yay.
We are interested in the largest ECU connector, nearest the driver's side fender. Pull out the slide clip thingy to unplug it.
Now we have to disassemble the connector housing. You will notice 2 purple clips on either side. Using a small pointy object or a safety pin, slide those guys out.
With them fully removed (don't lose them!), the innards of the connector will be removable. I did not take a photo of the rear connector cover piece. It is pretty simple, you just cut the zip tie and pop it off. With the connector disassembled it will look like this.
The pin we are interested in is number 39, the clutch switch input to the ECU. There are numbers on the outer connector housing to help you with the numbering, In this photo we are looking at pin 43 (at the bottom, green wire). Counting up 5 spots we come to pin 39, identified by the RED arrow. Note there is no wire here, which is why we must dig down this far. To remove the blank pin you use your pick or safety pin again and push up on the metal clip, identified by the BLUE arrow. Once that is pushed in, you slide the pin out in the direction of the ORANGE arrow.
Now we are in possession of a seriously tiny pin with no wire attached. Ta-da.
Grab a nice piece of wire. The size is important as it has to fit in the pin. I think the wire shown here is about 18 AWG, maybe smaller. The length will need to be 3 feet or so. Strip one end a get it to fit into the pin nicely. Like-a-so:
Then a quick solder job. You must be careful not to glob the solder on the sides of the pin housing, or any further forward than the wire goes, else it will not slide back into the connector housing properly. Ask me how I know this...
Not too bad for using hugely oversized tools for the job.
Now the pin slides back into the inner connector housing.
Reinstall the purple clips and then clip on the rear connector cover, replacing the zip-tie.
Plug the ECU back in and feed the length of wire down into the abyss.
This concludes Phase 1. You can now clip your ECU back down and reinstall all the plastic covers. Leave the battery disconnected for now.
Here are the final pieces that we need to get this done. We need 1 small butt connector and 1 small scotch lock. For my clutch switch, I harvested a vacuum vent switch (brake switch for cruise control) from a 1993 Audi 100 S automatic. Behold.
Drop the knee bolster in joe-audi (wait, this isn't your Audi? I hope you're getting paid for this crap.) and find the wire that you fed down into the car. Mine is red.
In this lousy picture I am showing the red wire is crimped onto one of the switch wires (black/green) using a pink butt connector. It is also showing the blue scotch lock which is connecting to the other switch wire (black/yellow) and tapping it into the brake light switch wire (black/blue).
Then the new clutch switch gets threaded into it's respective hole and adjusted "just right". So the switch is just fully depressed with the pedal at rest. Once it's plugged in, we are all done here. Make sure to zippy-strap your wires out of harms way before buttoning everything up.
Now you can reconnect your battery. Make sure to reset your dash clock and all your radio presets, cause that's important.
This concludes Phase 2. You may now try out your cruise control.
I now have functioning cruise control. Real, pure, OEM, not-from-concentrate Cruise Control. And it fricking WORKS. I should have done this months ago.
Also, I have noticed that this fixes MORE than just the cruise. Yes, you heard that right. With back to back testing I have noticed that having a clutch switch greatly helps the "throttle hang" issue when shifting at full throttle/high rpm. Whenever I would shift for example 3>4 at full throttle around 3000 rpm or more, the revs would actually go UP during the shift, no matter how careful I was with my timing of the pedals. I thought it was just my stupid-heavy OEM dual-mass flywheel. Such is not the case. This throttle hang and rev-up issue is 100% better now after the clutch switch install. I am excited to see if it fixes anything else. I do have another issue where my car likes to run like complete crap the moment I drop the clutch. Especially with the A/C on. Almost like trying to start off in second gear or something. It just won't get off the line unless I "launch" it. We'll see how that goes.