My cruise control works perfectly on some trips, or not at all on some trips. When it works, it does everything perfectly and turns on and off all day long, as long as I don't shut the engine off. When it doesn't work, it won't no matter how many times I try engaging it. It seems like it depends on something with the ignition when I start the engine. Could there be some sort of solenoid or something that is energized when the ignition is turned on, causing it to work great or not at all? It seems like this problem should point to something specific, I'm just sure where?

Look up some of the threads regarding resoldering the connections in the cruise control amplifier. Those things are really problematic, but resoldering everything in the amp usually fixes them.

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"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

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