Cruise Control Not Working
 

My cruise control has never worked in the 10 years that I have owned my 87 300E. I think it's about time to get it working. Where should I start?

BTW
I dont' mind getting used spare parts to swap out for trial and error..

The control unit is the usual culprit. It's under the dash to the left of the steering wheel.

Is that exactly what it is called? Cruise Control Control Unit?
I'm pretty sure I have seen it. It is a rectangular 1" thick metal and plastic box, right?

I just checked the website and that would be the cruise control amplifier, right?

Yes, and it looks like you described....

As you may have discovered from your search, the cruise control acutator may also be a culprit.

Where is the actuator located at?

The only symptom that I can recall from 10 years ago when I quit working was that it accelerated out of control. I had to kill the engine and roll to the side of road to restart the car. I have never messed with it since.

The actuator is inconveniently located under the intake manifold.

I'd try the amp first since you're part-swapping anyway.

Thanks. I'm going to the Junkyard, I mean the "land of used goodies" to find one.
It sure will be nice to take a little trip out of town and be able to set the cruise.

Before you burn up a good amp/ccmodule if you go to http/www.gdl-online.com you will find some easy to perform tests to help you verify what may or may not be the problem in your system. Really helped me, and if you wish Peter is really good about answering questions you may have.
My $.02.

Maybe this will apply to your model....
 

http://www.peachparts.com/shopforum/showthread.php?threadid=59250&perpage=15&highlight=stripped%20bolt&pagenumber=6


"Cruise Control on your older (80's) MB not working? Check all of your lamps first. If any are open (not working), replace them. The Cruise Control ground uses the lighting electrical ground. A burnt-out bulb will open the circuit and disable the Cruise Control (learned from the school of hard knocks - and a good MB tech)...Dutch"

Model:
1987-1988 Mercedes 300E, 300D, 300TD, 190D, 190E

Symptom:
Cruise control will disengage intermittently. Engine cuts out when vehicle comes to a stop.

Beginning with the production date of May 1987, the Hall-effect sensor, which is mounted on the speedometer, may have a defective cold solder joint on the sensor output pin.

If your vehicle exhibits these symptoms;

1: Cruise control will not engage at all.
2: Engaged cruise control will disengage intermittently.
3: Your 1988 vehicle cuts out when you come to a stop but will restart immediately.

Gently wiggle the output pin. If any movement is detected, the sensor is defective and should be replaced. After June 1988 an improved part was made (stamped 6.88) even though the part number remains the same.

Also wrong wattage bulbs in the tail lights may have also be the culprit. Some light bulbs fit and look the same as our OEM MB bulbs, but are actually different and will cause the cruise control to not function properly.

Or try reflowing the cold solder joint. Use a 25watt iron and a little rosin core solder. I'd rather fix than replace.

Maybe I'm cheap,

My 85 380SE had the same random acceleration and cut out problem. I fixed it by heating up the solder joints and adding a bit of solder to each of them. It worked best to heat each one up to burn off the corrosion resistant coating and then going back over with fresh solder. Works like a champ again.

A long held myth.

Read and learn:


http://www.gdl-online.com/begin1.html#contents