swftiii

Listers,

I need a little help. I'm trying to diagnose why my cruise control isn't engaging and found the following thread very helpful, but I've taken it a bit farther and would like to get thoughts from the EXPERTS.
https://rennlist.com/forums/964-foru...ontrol+Failure

This is what I have done:
At the plug for the Cruise Control module under the passenger seat, I've tested the following:
1. Pin #1 - Power - I get solid power (12.4v)
2. Pin #8 - Brake switch - 11.5v w/ brake pressed, 0v w/ brake out
3. Pin #14 - Clutch switch - slowly building voltage w/ clutch pressed, 0 w/ clutch out [expected readings are ~11.5v when engaged like the brake] (***THIS MAY BE THE ISSUE - AGREE?)
4. Pin #12 - Ground - 0 ohms
5. Pin #3 - Stalk 'Cancel' - 12.4v when pressed*
6. Pin #4 - Stalk 'Set' - 12.4v when pressed*
7. Pin #6 - Stalk 'Reset' - 12.4v when pressed*
8. I tried to test the plug that connects to the Cruise Drive on top of the engine (there are 7 connections), but I couldn't get any difinitive readings.
9. I have a fixed wing, so have the rear spoiler control module unplugged under the passenger dash, but tried plugging that back in to see if that affected the cruise and it still didn't engage, but the spoiler warning light did come on at speed - so I believe I've confirmed this is not an issue.
*The stalk pins had a voltage that was slowing building in mV until it would reach about 4v then it would go back to 0 and restart building (NOT SURE IF THIS MEANS ANYTHING, SINCE ALL 3 WERE DOING THIS)

Next Steps:
1. I'm guessing that the clutch micro switch may be bad and causing an issue since I believe it should read a solid 11.5v or so when engaged. Logically the readings sound as thought they should affect using the clutch to dis-engage the cruise instead of an issue with it engaging. Guess I'll replace this switch and see if that fixes anything. EXPERTS PLEASE COMMENT ON IF THIS COULD BE THE ISSUE.

2. If the microswitch isn't the problem, is there a way to diagnose if the problem is the control module or the drive? The only way I know how is to find a replacement control module to swap in - is there a better way?

3. Other thoughts? What am I missing.

Thanks...

-Skip

StanUK951

You don't mention if you have checked this or not but when my cruise control stopped working in the same way it was simply the throttle cable linkage in the engine bay. There is a small plastic cam type connector which connects the cable for the cruise control to the throttle cam. Sorry it's not a great description but if you look at where the throttle cable connects in the engine bay, if it is broken I think you'll spot it.

Hope that helps!

swftiii

Good catch I didn't mention it - it is installed as it should be.

swftiii

Update:

I also tested that signal is received from the speedometer via Pin #11 and that was fine.

So, I picked up a used cruise drive and control box the other day and because it is easier to replace the control box gave that swap a try first. So the test drive this morning and the cruise is working as expected. I'm very pleased and wanted to thank everyone out there for all your previous posts and sharing of knowledge so I could solve this at home.

Thanks,

-Skip

BigMikeATL

The very first thing to check is the switch on the clutch pedal.

Pull carpet back
Remove the board on the floor

The switch is under the clutch pedal. Mine was sticking and I sprayed it with contact cleaner and worked it a few times. Now cruise works fine.

Greg_V

Don't post here much but I had the exact same symptoms as swftiii on my 1992 964. Turns out it was LED brake lights I had installed. The 928 shares the same CC module. I stumbled across their thread on CC and LED tail lights when I had not yet found a CC to swap as a test. https://rennlist.com/forums/928-foru...ke-lights.html I changed out the LEDs for incandescents and the CC works just fine. I have not tried to the a 928-like ground mod to enable LED tail/brake lights.

Vandit

Hey, got your PM. I had read this thread earlier and wondered the same since I run an LED 3rd brake light bulb. My cruise control still works. My car is a '91. Maybe something changed w/ the electronics in '92?

Greg_V

Cruise control confirmed to work with LEDs brake and turn signals upon the following wiring modification:

On the body side wire harness that runs to the left rear tail light housing:
Run a 6 Ohm 50W resistor in parallel with the harness connector, between Brown and Grey/Black on the for brake LEDs, Black/white and Brown for turn signal LEDs

On the body side wire harness that runs to the right rear tail light housing:
Run a 6 Ohm 50W resistor in parallel with the harness connector, between Brown and Grey/Red for brake LEDs, Brown and Black/Green for the turn signal LEDs.

There is not a lot of room behind the corner lights, so i added a length of wire to route the load resistor to be behind the center reflector.

vasculardoc

I'm thinking of upgrading to LED's - can you possibly post a photo of how this wiring setup looks so we can see exactly how this looks (for us minimally car electically educated dolts ! :-) ) and so we can replicate it.
Thanks in advance.

Mark

Greg_V

Here you go Mark. Hope this helps.

Greg




resistor mounted behind center reflector





wire taps on the car-side of the corner lights

vasculardoc

Thanks :-)

Greg_V

My pleasure Mark. The resistors go in parallel to the bulb, if that wasn't clear. Note that I used stainless steel zip ties. The resistors get hot enough to burn you, so something heat resistant is a must. I saw on another thread that someone had some luck with finding a bulb that didn't require a load resistor. Don't know how that affects the cruise control, or not, however.

https://rennlist.com/forums/964-foru...ear-bulbs.html

Alexd912

Hey,
I hope someone is still reading this thread.

So my cc is not working as well, but thanks to all the hard work on this post I managed to find that Pin #3 - Stalk 'Cancel' - 12.4v when pressed*, is actaully 12V constantly and drops to 0 when I press the stalk!

Before I start to remove the switch gear could there be any obvious reason why this could happen?

Cheers

Alex

ToreB

Wow, that was a thread revival indeed. As far as I remember is the cancel/off switch a normally closed switch to +12V, so your reading of 0V when switch is activated is fine.
The most common cause for CC problems is a misplaced clutch pedal switch.
Cheers,
Tore

JohnK964

Just about ten years ago when I got my car 91 C2 Tip
the cruise control worked but disengaged at at the time were odd intervals. I’m slow but after the 3rd time I realized it would disengage when ever I signaled a lane change to the right. Long story made short a previous owner added a 3rd brake light and connected the ground of it to the ground of the turn signal. Seems picky to a non wiz like me. Tore ( god bless him ) probably will read this and say oh yea and have the correct explanation.