I am getting no response from my cruise control. It is the last item on my list for getting my recently purchased 300E back into tip top condition.

Can anyone give me some advise on how to trouble shoot the system? I have alldata.com but they are very weak on cruise control.

Thanks and smiles.

Firstly, do a search on cruise control through this site. I addressed this very problem on my 300E recently. Mine would either not turn on, or it would simply shut itself off within a few seconds. I did a posting and JCE responded with some very helpful advice. First and foremost, check ALL of your light bulbs on the back end of the car to see that they are the correct type. If they aren't, it can have a negative effect on how well the cruise works. I went ahead and replaced ALL of the rear bulbs........and, voila!, the cruise control began to work. Pretty neat trick. Make sure you use OEM bulbs like OSRAM. If this doesn't take care of the problem, then it gets a little more complicated. Actuators and Amplifiers. A little over my head.

On the 1985 300D I have been experiencing intermittent cruse control operation. Sometimes it works and sometimes it doesn't. It seems to be dependent on the outside ambient temperature. Works just about anytime the outside air temperature is above 85 degrees out. I took the cruse control amp out and looked at the circuit board. There is no doubt that 15 years of south Georgia heat has taken its toll. The circuit board has that "old" electronics smell that I had not smelled in years. I replaced all of the rear light bulbs but this does not seem to have made any difference. I will probably try a rebuilt amp from Fastlane.com over the next few weeks unless someone on here has another thought or suggestion. The linkage under the hood is well lubed and the worn pieces have been replaced.
thanks
Jim
'85 300D
'95 E320
'97 CRV

I'm having the intermittent cruise control problem as well! I'm going to replace the bulbs and see if that fixes it! Thanks Primo! I love this site!

I did have the same problem, intermittent operation, replaced the amplifier, 1/2 hour, easy job, it is under the dash on the driver's side. Problem solved. Good luck.

Alex

I removed the black insulated covering under the dash (above the floor) at the driver's side but could not find anything resembling an amplifier. Do I need to remove more of the dash?

Smiles.

Cruise control diagnostics on internet....
 

Hi EJ,
Take a look at this site: http://gdl-online.com/begin1.html#contents
GDL seems to have the most comprehensive and accurate diagnostics for troubleshooting the cruise control system on the internet, and was very helpful in fixing my unit. Their rebuilt amplifier units can be "desensitized" for smoother operation, if you request same at the time you order. In my case, the actuator motor was defective, but either the amplifier or the actuator could be the source of your problem. By using their troubleshooting info, you can determine what you need pretty quickly. By the way, the amplifier is mounted next to the steering column and on my '82 was retained by a single 10mm screw. It has a 14 pin connector and is an aluminum box about 1 1/4" x 4" x 6.5". It is hard to get to due to it's location.
Richard Wooldridge
'82 300D/4.3L V6
'74 280C
'77 Jag XJ6
'77 280Z

Hi Richard,

Thanks for the link to General Development Laboratories! They are obviously one of, if not THE authority on this issue. It looks as though they have the solution to any cruise control related problem.

It was interesting to see the "bulb myth" section. For me, that was the fix with my system. I did use OEM/Osram, but I guess it didn't matter. It only matters that the bulb is good and that it's doing its job being a link in the chain.

Thanks again for the link to gdl-online!

Primo

Amplifier location....
 

Hi EJ...
After rereading the GDL info, I noticed that they indicate your amplifier could be located under the passenger side foot rest. Hope this helps...
Richard Wooldridge
'82 300D/4.3L V6
'74 280C
'77 Jag XJ6L
'77 280Z

Yes Richard I think you may be right about that passenger side location. I had the flooring up a couple of weeks ago tracing for a corroded connector in the central locking system and noticed all kinds of electrical mystery boxes under there. I will most definately check out GDL.

I hope to have a diagnosis by the end of the holiday.

Mucho Gracias!

Smiles.

Earl,

I have checked the component location for your model in my MB Electrical Troubleshooting Manual just to be sure. The amplifier is located "Behind lower left side of dashboard."
I have the one I removed from my 86' 300E in my hand: it is a silver coloured rectangular metal box, dimensions: 6x4x1.5 inches. There is a 14 point connector at the front. Made by VDO.
To get to it remove the headlight switch, remove the black mooulding along the dash on both side of the steering column (under whitch you will find the screws holding the dashboard cover), unhook the hood release and the handbreak cable and remove the cover just below the dashboard.The amplifier is located just left to the steering column secured by two screws to the bottom of the dash. You can also follow the instructions on the GDL site. They are quite good.

Alex

Ok Alex... that bit of info saved me a lot of grief. Now I have to trouble shoot the system to determine what the problem is!

Smiles.

I get the same conflicting information regarding the location of the amplifier. The only hunch I have is that there are some changes on the 300E begining in May 1987. These changes may effect the location of the amplifier. Does anyone have an insight into the question?

I guess the easiest thing to do is to tear up the floor first!

Smiles.

Earl,

The passenger floor is easy to access. Pull up the carpet insert, it has snap-like attachments in each corner right in front of the seat. Then pull up the plastic floor panel, then remove the foot panel.....it maybe has a screw on the bottom, and it attaches higher up with a clip. At this point you'll see several wiring harnesses and then maybe your cruise amp. Hope this helps.

Good luck!

Primo

I just had my amp repaired by
 

GDL and they are an excellent company to do business with. Prompt, good communication and good price for repairs.