My 124 cruise is UNcontrolled
 

I've followed all the troubleshooting steps for the cruise control on my 1989 260e;

-checked voltages
-checked continuities
-checked current draw
-resoldered amplifier
-cleaned pins

But I didn't fix anything. Sometimes (10% of the time) it will accelerate when I lift the stalk upward and hold it there - but only from a cold start. And only once. After I stop accelerating - say for a school bus or a dog crossing the street - it will not do anything again on that trip.

However, last week I had the local MB dealer do a 4wheel alignment (I just put on new shocks, struts, tires). Driving home from the dealer, I went through my routine test of the cruise just to see if it will accelerate - and lo-and-behold - it held at 67mph perfectly! It accelrated a couple MPH with each tap upward and decelrated with each tap downward. I was tempted to keep on cruising down I-90 just to see how long it would hold, but I had to get home. I cancled the cruise and exited the highway. I tried setting it again on a straightaway at about 40mph. And it held. I tried accerating - and it died. And hasn't worked since.

Is it just coincidence that it worked immediatly after the alignment? I gotta' think that is the case. If not, it would still be working - right?

Do a search on this topic. Mercedes of that era had a problem with the PC boards either cracking or solder joints breaking.

Open the box and test circuit continuity. Solder all broken connections and VIOLA!

Sounds like it needs a new cruise amp, or electronics repaired inside. The dealer has a CC testing that tests everything EXCEPT the computer. If it finds no faults, then by process of elimination it is the computer (amp). New amps are around $300, some offer rebuilts for $200.

Did you check the switch? I recently went through the same thing, however I did not try the resolder as they won't accept the core for rebuilding if you do. If you checked the switch signal in addition to everything else, you probably need an amp. I sent my amp and actuator to GDL and it's on the way back as I type. My actuator was OK, but I sent it just to be sure because a faulty one will blow an amp. You may try a salvage yard as you just might get lucky. Look for low milegae cars. I couldn't find any 14 pin amps but I found a dozen 10 pin. That's my luck. Even if you find an amp that doesn't work, you could use it as a core for a rebuild. If you find one in a 'pull your own parts' kind of place, refer to it as a 'cruise control switch relay' - do not use the word computer or amp (save $$) And you never know, you might get lucky and find one that works.

Time kills these things more than miles. I'd focus on a rebuilt or new amp rather than finding a used one that works. you could use a used to to see if it changes the problem, though - if it does, its probably the amp and not the switch.

I tested the switch and it checked out fine.

I'm hearing from all you folks that the CruiseAmp is the suspect. I guess it makes sense because the case of the one that I have now (the one I resoldered) was marked with a grease pencil indicating it came from a junk yard.

I like the idea of pulling one from a yard, seeing if it works, and if not, using it as a core for replacement.

I think I may double check mine and see if I can see any bad solder joints that I missed.