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1979 deVille cruise control malfunction - help!

2665 Views 4 Replies 4 Participants Last post by  Night Wolf

Have a '79 Sedan deVille with 77k miles. Cruise has always worked fine until Monday when I set the cruise and instead of holding the speed the car started accelerating steadily and would not stop until I stepped on the brake. I tried again and the car did the same thing. Anyone have an idea of what may be causing this?

Thanks in advance for the help!

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If you haven't done it already, it's probably a good thing to check and clean all the electrical connectors associated with the cruise, as well as the vacuum lines. My unit had a vacuum line that was off.

The shop manual says for "erratic engagement and/or unwanted program acceleration" to check for "severed engage switch harness in column", or "open circuit in yellow wire at connector."

It's probably something simple, either a wire or vac line. The trick is finding the right one. Check your fuses too.
Problem is likely either the engage button at the end of the directional signal stalk sticking slightly in the "resume" position, or there's an open connection in the steering wheel column as suggested above. Obtain a FSM and start diagnosing. You have an awesome car. Good luck.

Thanks Highway Star and 77 CDV!!! We are going to tackle the cruise issue this week and I will report back with what happens. Your ideas are invaluable! We luckily have the service manual. Again, I really appreciate the assistance!!!!! Dave
Ah yes... same exact problem on my '79 when I got it..... it was quite funny to show people in the car the 1979 version of cruise control.... heh...

anyway, the cruise control moudle on the valve cover... I went to the junkyard and got a new one, then it worked... but... turned out the wire harnesses were kinda coroded from time... get a wire brush, unplug the connectors, clean them up, then get dielectric grease and put it all back together, it should work great :)
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