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Old 12-03-2008, 02:30 PM
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Join Date: Dec 2008
Posts: 3
cruise control acting funny


I have a 1987 420SEL and the cruise control is kinda working. Let me explain. When you set the cruise lets say at 65mph it sets and then accelerates to 80mph. If I try to use the lever to decelerate nothing happens. I did not let the car cruise at 80 as I dident want a ticket, so I cant say if it held speed or not. I can say it stopped accelerating when it reached 80.

Any help would be welcome.

Thanks Paul

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Old 12-03-2008, 08:46 PM
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Join Date: Sep 2004
Location: Seattle
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What happens if you set at at 45?
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1988 F150 144,000 miles (leaks all the colors of the rainbow)
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Old 12-04-2008, 08:16 AM
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Join Date: Dec 2008
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If I try to set the cruise at 45 it seems it dosent work at all.

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Old 12-04-2008, 08:22 AM
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Join Date: Apr 2006
Location: Arlington, VA
Posts: 7,190
Is there one particular component in the cruise control that is most prone to breaking/wearing out? The CC on my 300TD seems to work periodically. I haven't noticed a problem like you described, though. The SEC's CC doesn't work at all. It's waaay down the list of things to fix, though.
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Old 12-04-2008, 08:25 AM
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Location: North Wales, PA
Posts: 4,001
On the w123's it's usually the cruise control amp ... just ask JimmyL.
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1998 Acura 3.0 CL
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Old 12-05-2008, 08:06 AM
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1983 300SD, 4 speeed
Join Date: Jul 2006
Location: Raleighish, NC
Posts: 664
The cruise control amp on a w126 is located under the dash about knee high on the driver's side. Remove the kick panels and lay on your back upside down in the driver's seat. I think it is a 10mm bolt and a phillips screw. It is a square silver (aluminum) box 4-5 inches long 3-4 inches wide and 1-12/3 inches thick. Leave your keys in the ignition, find the buzzer, look at the box next to it. There you go. Remove your keys, have fun. These are known to go bad. Look at the top, carefully bend back the ears and slide the circuit board out, clean the circuits, look for burned or cracked connections. You can try to resolder the amp or buy a new one. I have found a few in the junkyards that keep going. Start by cleaning the connecters with alcohol swabs. Test it out, go from there. Good Luck.
If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
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Old 12-05-2008, 06:08 PM
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Join Date: Oct 2007
Posts: 1
I had the same issue with my 1990TE-intermittent engagement, surging, turning off, etc. I removed the amp and everything looked OK on the board. SO.... got out the solder gun and hit every solder joint, with exception of IC boards. Even did the 90 degree plug to board joints. To my utter amazement, it now works great. Good luck

Last edited by Boregards; 12-05-2008 at 06:09 PM. Reason: spelling
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