86 560SL Cruise Control

[MRB]

I am new to the Club, so this question may have been asked in the past.

The cruise control on my 86 560SL does not work. I have replaced any non-original light bulbs with factory new bulbs. I was told that this could affect voltage.

Recently the battery died due to two dead cells. Just prior to this, the cruise control started working normal, so it appears that the actuator does work.

Also, it appears that the auxiliary fan never comes on.

Any suggestions?

[kropsch]

Go to the archives where you can find lots of good information.
A good one is

http://www.gdl-online.com/testproc.html

[Peter D. Quinn]

To MRB:

It sounds like your car needs a going over, as I don't believe there's any cause and effect between your battery going dead, the auxillary fan not working and the cruise control being inoperative. Let's try to address a couple of them.

First, it's good you got the battery squared away, as that can make your electricals act whacky when operating under low voltage.

Next the cruise control. While there are a number of components to the system, the thing that is the most frequent problem is the amplifier, which will either just die, or will be erratic, then die. It's a silver box about the size of a pack of cigarettes located up under the dash near the steering column on many cars -- not sure about yoru SL. Replacements can be purchased from George Murphy -- last one I bought was something like $150. The hardest part about replacing it is that after taking off the lower dash panel you have to get in almost upside down to get to it, take it and it's bracket out of the car, replace the amplifier on the bracket then re-install.

I believe the auxillary fan has 2 things that will trigger it, one being the AC system, the other being a temperature sensor on the engine, to provide extra cooling when needed. The first thing I'd test is to see if the fan itself works, i.e. try to feed 12V power to it & see if it'll run (this after checking that the fuse that controls the fan is good). After that, perhaps others on this List can advise how to check other functions, as that gets out of my league.

One other thing: if you haven't already done so, go to a MB dealership and get 2 or 3 packages of assorted fuses, open up your fuse box and one by one, pull out the old fuse, clean the fusebox contact if necessary, and put in a fresh fuse of the right color. When fuses get to be 10+ years old they can look fine but not be conducting electricity properly and can cause lots of mysterious electrical problems. At a cost of only a few dollars it'll save you many headaches. And, it's easy.

Hope this helps, let us know how you do.

[MRB]

Paulo Kropsch and Peter D. Quinn,

Thank You very much for the information. I now have a starting point to trouble shoot this problem.

M. Bennett

[archiele]

Originally posted by Peter D. Quinn

Next the cruise control. While there are a number of components to the system, the thing that is the most frequent problem is the amplifier, which will either just die, or will be erratic, then die. It's a silver box about the size of a pack of cigarettes located up under the dash near the steering column on many cars -- not sure about yoru SL. Replacements can be purchased from George Murphy -- last one I bought was something like $150. The hardest part about replacing it is that after taking off the lower dash panel you have to get in almost upside down to get to it, take it and it's bracket out of the car, replace the amplifier on the bracket then re-install.



So would you say, if the CC starts to surge gently then after about 10 miles it drops out, that the amplifier is the most likely culprit?

[Peter D. Quinn]

When your cruise control starts to act whacky (that's a technical term :) ), i.e. being erratic, cutting in & out, or finally just failing completely, the most frequent cause is the amplifier. While there are other components in the system, they rarely are the culprit. If your system is 'dropping out', as you say, sounds like you need a new amp.

The surging can also be another issue, i.e. if your throttle linkage isn't well lubricated & is binding, it won't move smoothly and it will make it feel as if the system is surging, being jerky. Lubing the linkage is supposed to be done on a frequent basis.
pdq