Clutch Switch for Cruise Control

[megerian]

My cruise control has never worked. Thought about buying a new "brain" but since they aren't cheap, and searches through this forum cited the clutch switch as the next most likely culprit, I thought I would take a look at that first.

I first verified that the fuse and relay are fine.

Then I disassembled the driver side floor boards. By the way, Bentley manual only talks about the pre-87 cruise control, and I have an '88 with the electric servo, so Bentley wasn't much help.

Anyway, the point of this post is to ask about accessing the clutch switch. Its virtually inaccessible, even with the floor board removed. I contorted myself into the floor compartment, and still could *barely* see the edge of the switch. I thought I was onto something, because the switch didn't look like it was lined properly on the piece of metal that moves when the clutch is depressed. So I thought that the problem was simply that the switch always thought the clutch was depressed, and hence the C/C never worked. I reached in there, and tried to line it up a little better, but to no avail, since I put it all back together and the C/C still didn't work.

Question : is there a better way to get access to that little switch other than from the right side of the pedal cluster? I just don't see any way to even see the thing, let alone remove/inspect it.

[Por_sha911]

IIRC, the switch is electrical that either sends or interrupts a signal to the cruise brain. If this is the case, find out if the switch is opening or closing the circuit and then you can either jump the wires on either side or disconnect a wire... That will reverse the action of pressing the clutch and you can check the cruise. This is more conjecture than experience so if nothing else, you get a free bump.
I can tell you from experience and reading that most cruise problems go back to the brain having bad solder joints or a burned capacitor. It is a 5-10 minute job to swap with another car. Got a buddy with a similar unit? Look up your local PCA president and he'll know someone.

[Crude Rudy]

Remove the peddle assembly and rebuild it, during removal you have easier access to the switch. Also triple check that the small vacuum hose is properly attached to the cruise vacuum accumulator next tot he fuel filter in the engine ares

[Por_sha911]

Why rebuild a peddle assembly if all he needs is a cruise brain? It is always wiser to diagnose the problem rather than just throw parts and money at it and hope something gets better.

[DRACO A5OG]

Post a pic of the Cruise Control Module in the engine bay and to to focus on the two attached hoses, particularly the smaller OD hose connected to the T connector of the Vacuum line.

[megerian]

This is an '88, so no vacuum hoses, just an electric servo. Looks nothing like the pix in the Bentley. So I figured its much more likely to be either the brain or the clutch switch, and thought the clutch switch was easier to troubleshoot first..

[porschenut]

To access the clutch switch from above, pull the carpet back off the tunnel. there is a big hole in the top of the tunnel that allows access to it.

Pull your Bentley back out and read the page with the CC troubleshooting steps. With a multimeter, you can check all the components and determine where the problem likely is.

Crude Rudy, the clutch switch in the 78-later cars is inside the tunnel, not on the pedal cluster like on the early cars.

[DRACO A5OG]

Originally Posted by megerian

This is an '88, so no vacuum hoses, just an electric servo. Looks nothing like the pix in the Bentley. So I figured its much more likely to be either the brain or the clutch switch, and thought the clutch switch was easier to troubleshoot first..

So you don't have the servo and cable connected to the throttle body in the engine bay? Strange?

[megerian]

porschenut, thanks, I will look there. Do I need to remove the console?

Draco - there is a servo and a throttle cable. I can post the photo. I just meant that there aren't any vacuum hoses, so it looks completely different than the pre 87 servo.

[DRACO A5OG]

whoa, just learned something. thanks

[porschenut]

Originally Posted by megerian

porschenut, thanks, I will look there. Do I need to remove the console?

You might have to remove the console, I can't remember as it's been a while since I was last in there. You'll have to just peel the carpet back and see. As I recall it was quite easy to get access to the clutch switch from there.

[kodioneill]

Just check the clutch switch at the ECU connector. You can send out the ECU and have it rebuilt for $90. It is most likely the ECU that is bad.

[megerian]

Dusting off an old thread, because my cruise still doesn't work, and I would like some suggestions on what to try next. This is what I have done already:

- Since the cruise module is a common cause of issues, I sent it out to be rebuilt. It was sent back fixed, along with a video showing that it works correctly in his bench testing setup.
- Installed the rebuilt module, still doesn't work. Cruise does nothing at all.
- Using a voltmeter, and following the troubleshooting guide I can verify that at the wiring harness the cruise stalk functions are working.
- I also verified that the brake and clutch are triggering the correct behavior according to the troubleshooting guide. Specifically, connecting terminals 1 and 14 in the plug receptacle, the reading goes from 12 to 0 when I press the clutch. Connecting terminals 8 and 12, the reading goes from 0 to 12 when I press the brake.
- I am not able to verify the ohm readings, either because I don't know how to use an ohmmeter, or because there is actually a problem.

At this point, I almost feel like the only step is to find someone with an '88 and with working cruise and swap the modules, to see for sure if the cruise module works.

Here are some (possibly naive) questions:

- Can the wiring receptacle show all the correct readings, and the module be working perfectly, and the cruise still not work due to a cable or other failure later in the process? If so, what can I check next?
- Since all the voltmeter checks pass, and I watched the video of the working module, can I be 100% sure that the module works?
- When the voltmeter checks fail, its obvious what the problem is (clutch switch, stalk lever, etc.) but if the ohmmeter checks fail at the wiring receptacle, what would that indicate?
- Anything else I am missing?

[megerian]

Also, these are the ohmmeter checks listed in the troubleshooting guide:

Connect ohmmeter to ter.11 and 12, push car slowly. The reading should alternate between 0 and infinity
Connect ohmmeter to ter.5 and 8, reading should be approx 30-40 ohm
Connect ohmmeter to ter.7 and 10, reading should be approx 2-6 ohm
Connect ohmmeter to ter.9 and 12, reading should be 2-4 kohm
Connect ohmmeter to ter.12 and 13, reading should be 2-4 kohm

What would failures of these tests indicate?

[Hendog]

Originally Posted by megerian

Connect ohmmeter to ter.11 and 12, push car slowly. The reading should alternate between 0 and infinity this is likely a flywheel sensor, so basically ON/OFF.
Connect ohmmeter to ter.5 and 8, reading should be approx 30-40 ohm
Connect ohmmeter to ter.7 and 10, reading should be approx 2-6 ohm
Connect ohmmeter to ter.9 and 12, reading should be 2-4 kohm
Connect ohmmeter to ter.12 and 13, reading should be 2-4 kohm

What would failures of these tests indicate?

I don’t know what the other readings determine, however it owuld still be good to know what your readings are. If they are vastly different then I would look into the significance of those points. What make/model of meter are you using? Could possibly coach you on how to use it.

[brianlay]

Do you know when it last worked?

[megerian]

No, it has never worked in the 6+ years I have owned the car.

[brianlay]

Ok, I see that now...didn't realize you had revived your own 6 year old thread.

silly question...there is a servo and it's plugged in? And an actuator cable connected to the throttle body?

If so, then you've got to confirm that the servo motor is electrically connected to the Cruise
Control which is done with the ohmmeter checks.

You already confirmed the CC stalk, brake switch, and clutch switch are working, correct?

If you've had the control unit repaired/verified and the switches are working then the problem must be with the servo and/or wiring.

Hopefully it's a wiring problem because a replacement servo from our host is over $800.

I can walk you through the ohmmeter checks when you're ready.

[megerian]

I have verified that the CC stalk, clutch switch and brake switch are working, by using the voltmeter tests on the disconnected wiring receptacle.

Here is the cheap multimeter I bought, and I am not sure on the ohm tests. For one thing, the crude instructions say to switch it to 200mA and I don't know if thats a typo or if that means 200 in the ohm section. (yes, i know nothing about using a multimeter)





In these photos I am showing what I think is the cable to the actuator, although I am not 100% sure. Some of the manuals say the actuator is in the front left wheel well.




If the actuator was faulty, would the ohm tests indicate that?

[Chuck.H]

My clutch switch has needed adjustment periodically - I can usually verify this by using my foot to pull up on the clutch pedal, thus releasing the switch and letting the CC engage.

I think I have been able to access the switch by removing the accelerator pedal and peeling back the carpet (may need to unbolt the console and at least shift it off to the side a little).

I also recall I've been able to just bend the tab into position rather than reposition the switch.

HTH,
Chuck.H
'89 M491 Targa, 440k miles