560SEL - Demon possessed cruise control
 

Okay so my 1989 560SEL's cruise control has become possessed. It started about 4 months ago. At first it started not engaging at all. It just stopped working. Then it started working sporadically. Then is started working but setting its own speed. Then it started working fine for a few miles then shutting off. What the heck is going on with it??

Time to re-solder/reheat the control box PCB joints. Do a search to find the details. There are test procedures to pin-point the cause, ie. ruling out the actuator, the speed signal sensor, vacuum, wiring, etc., all found in the shop manual, but it would seem from the number of posts here on this subject, the solder joints in control box are usually the problem, from the symptoms given.

I did mine twice. First time, I got 1 1/2 seasons before it started acting up again. Second time, 2 seasons, and maybe this one coming up too.....of course, you can get a rebuilt one for under $200.00, or try your luck with a junk yard donor....

what exactly is the unit called. I'd rather just buy a new one and be done with it.

Its called a cruise control amplifier.

Here they are on the Fast Lane parts site:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=29T0268BS2BC0ZLNJ4&year=1989&make=MB&model=560-SEL-001&category=P&part=Cruise+Control+Amplifier&appChassis=A311370-A999999

Or, since there appears to be different ones for a 1989 560SEL, I would call Phil or Roy at fastlane and give them your vehicle number and I bet they can look up/get you the right one.

I had mine repaired for $40 by a fella on this forum, David Pryce, I think. His company is American Controls Corp. in Houston. A search should produce the thread where he volunteered to do this for forum members for a slight fee. Beats the $300-400 for a remanufactured one! Mine still works fine two years later.

did a search couldn't find him. Ideas?

My advice FWIW: get it rebuilt by GDL. Set you back just over $200. Just had mine rebuilt by them after considering all the options ($40 solder job, new one, used one, etc..).

Go to http://gdl-online.com/begin.html.