[968TDG]

Hi everyone. I just drove 2,000 miles without cruise control from St. Paul Minnesota to Oceanside, California. I bought the car last week. The owner claims that the cruise control has always worked, but I have had no luck.

Before I got to far into it, I just thought I'd ask in case anyone has had any luck with sorting out a non-functioning unit.

So, I tried to press the stalk towards the gauges, it moved but nothing happened. I moved it in all directions with varying amounts of force, and nothing happened. I read the directions, I checked the fuse for it under the hood, I kept on moving it around hoping that it would magically start working (you get bored driving 2,000 miles)

Any advice?

Thanks [img]style_emoticons/<#EMO_DIR#>/rolleyes.gif[/img]

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[flash]

a number of things can make it fail to operate - the cable that goes to it is known to get out of adjustment - a short in the brake lights will do it too - even when it works, it operates a bit oddly, and there is no indicator on the dash

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[flash]

if you continue to have trouble, let me know - send me a pm with your number and maybe we can figure out a time for you to pop up here and i can try to figure it out - i'm not far away - lol - who knows? maybe by that time i will have dragged the TR-4 over here and started her clean-up - i've been meaning to get started on it and have been dragging my feet

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[Anchorman]

There are also interlock switches on the brake and clutch pedals that, if not set correctly, can prevent the system from operating. And then there's the cruise control "brain" - which I've had replaced twice over the last six years (IIRC, it's located under the dashboard, to the right of the steering column - they are so prone to failure, primarily from cold solder joints, that I currently have two spares). The only time I've gotten a speeding ticket during those six years was when the system stopped functioning during a long drive. I'm a major user of cruise.

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[Cloud9...68]

Mine has never worked, either. I've never missed it, as I never take the car on ong trips, and I've never found cruise to do much for my lap times [img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img] , but I'll be interested in what solutions come oout of this thread, in case I ever get ambitous enough to tackle it.

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[josephsc]

Another component that often fails is the cruise control servo (in the engine bay to the passenger side, where the cable adjustment is) -- there are electrical contacts inside the servo that just gets worn out over the years.

But my first bet would be the computer (driver-side footwell, outer edge, under dash -- need to be a contortionist with small hands to reach the two 10mm nuts holding it up). I would personally start by borrow a computer (from a 968 or any post85.5 944) that's known to be good.

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[joeh944]

An incorrect brake light bulb can also disable the cruise control (don't ask why I know that [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img] ). Good luck.

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[968TDG]

Haha so pretty much check everything!!!

Fuse
cable adjustment
brake light short
incorrect brake light
interlock switch on the brake pedal
interlock switch on the clutch pedal
cruise control servo
cruise control computer

at least that keeps it interesting, I wouldn't want the solution to be too obvious (-:

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[968rz]

These are very similar (if not the same) control units as the 944 and one common issue is the cold solder joints crack, the fix for this is to dis-assemble the controller and re-solder all joints and the PCBs.

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[kwikt]

<!--quoteo(post=77056:date=Aug 6 2009, 04:30 PM:name=joeh968)-->QUOTE (joeh968 @ Aug 6 2009, 04:30 PM) <{POST_SNAPBACK}><!--quotec-->An incorrect brake light bulb can also disable the cruise control (don't ask why I know that [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img] ). Good luck.<!--QuoteEnd--><!--QuoteEEnd-->


Also check the 3rd brake light bulb. A burned out bulb CAN cause the cruise control not to work. Check fuses!!!

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[DAK]

Check the wire to the clutch pedal switch first, it is easy to see. Mine was broken once, apparently by my left foot. It is a cinch to reconnect the wire then ziptie the excess up out of the way.

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[Mark]

<!--quoteo(post=77056:date=Aug 6 2009, 06:30 PM:name=joeh968)-->QUOTE (joeh968 @ Aug 6 2009, 06:30 PM) <{POST_SNAPBACK}><!--quotec-->An incorrect brake light bulb can also disable the cruise control (don't ask why I know that [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img] ).<!--QuoteEnd--><!--QuoteEEnd-->


<!--quoteo(post=77275:date=Aug 10 2009, 01:18 PM:name=kwikt)-->QUOTE (kwikt @ Aug 10 2009, 01:18 PM) <{POST_SNAPBACK}><!--quotec-->Also check the 3rd brake light bulb. A burned out bulb CAN cause the cruise control not to work.<!--QuoteEnd--><!--QuoteEEnd-->
Really? That's nuts.

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[flash]

not unimaginable - the brake circuit interrupts the cruise control - the brake light switch is the key here - if there is a short in the brake lights, it trips the circuit - a blown bulb could create said short

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[Cloud9...68]

I just checked Clark's Garage, and the only thing he suggests as the cause of a non-functioning cruise control is the computer itself, and he gives a procedure for removing it, and checking the solder joints, which he says can sometimes deteriorate over time. I think I'll check the wire to the clutch switch first, though, since this sounds very simple. I've already checked the fuse, and it's fine. What exactly is the clutch interlock switch, anyway, and why does the operation of the clutch have anything to do with the cruise control? Thanks.

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[flash]

if the clutch did not disengage the cruise control, the engine would race when you stepped on the pedal

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[Cloud9...68]

Doh! Yes, of course, that makes sense. The good news is that one of the wires to the clutch interlock switch was indeed broken, so I'm hoping that's all that was preventing mine from working. I'll test it out tomorrow...

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[Cloud9...68]

First the good news - Sure enough, one of the wires going to the clutch switch was broken at the connector. I installed a new connector, and voila! the cruise control now works!



...Sort of.



It does work, apparently for the first time in years, but when I press the clutch when the cruise is engaged (which strikes me as a somewhat illogical thing to do), the engine races at an alarming rate to the redline - I have to step on the brake to stop this.



So, from reading some of the other cruise control posts, it appears that my clutch switch is broken, right? It looks simple enough to replace. Has anybody done this? Any tips/pitfalls to avoid? Is the switch very expensive? Thanks.

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[DaveN]

When you press the clutch the gas should drop to idle not redline as that is the whole point of the switch. Get out your DVM and test that switch, sounds like it's permanently stuck in the correct position to keep the cruise happy but fails to change state when pressed.

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[Cloud9...68]

Mine is intermittent. Sometimes the rpms drop back to idle when I press the clutch with the cruise engaged, but most of the time it wants to run to the redline (until I stop the fireworks by tapping on the brakes). So, I'm sure the switch is bad. I'll call Sunset tomorrow to order a new one. Hopefully it's available, and not too hard to replace. Thanks.

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[flash]

it could be simply dirty - if it's like a lot of brake light switches, it's just a plunger switch behind the pedal - see if you can get in there with a can of contact cleaner - i'll see if i can take a look at mine today

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