The vehicle is an '83 300D. Last Wednesday I installed a new/remanufactured cruise amplifier in an attempt to fix my completely unresponsive cruise control. The following day the cruise worked flawlessly over an 8-hour/500-mile period. The thing is, a few hours after finishing that drive I took the car on a much shorter highway drive and the cruise started acting up - it wouldn't set to the speed I selected, but would accelerate up to about 75 mph and then decelerate slowly until it finally disengaged completely. I've tried it a few more times since then and it has continued to act up.

At this point I'm thinking that the actuator must be bad, but I can't figure out why it would have worked so solidly for over 500 miles only to start acting up just a few hours later???

Maybe, but the amp failed sooner.

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83 SD

84 CD

For probably half the price of a rebuilt cruise amp you could get an entire modern, brand-new, warrantied aftermarket cruise control system. Wire it up to your existing control stalk and you'll never know the difference - except the thing doesn't have 1970's electronics in it and it'll actually work.

Relevant thread here.

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

here's my aftermarket cruise install... The Official Audiovox CCS-100 Install Thread

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Mike
1983 Mercedes-Benz 300SD 270K
1960 Ford F250 62K
1990 Mazda Miata 156k

The thing is Bob, it's not that I'm lazy, it's that I just don't care.