need some help with electric wiring on 1968 250SE

[zdzich]

Hi. I have a hard time to find the wiring diagram for my 68 Mercedes 250SE. There is one wire that goes to a switch located on the firewall just behind the valve cover. I don't know what the switch is for and where it should be connected. Please see the attached picture. I marked the switch with a yellow arrow. Thanks for your feedback.

[ja17]

Most likely it is to activate the deceleration solenoid on the injection pump.  If so your injection pump has two solenoids on the back end.  The lower one is the deceleration solenoid. In many cases these are left disconnected since it is primarily an emission related device and may cause problems if they malfunction. The device moves the injection pump rack to full lean when the accelerator pedal is at rest.

[zdzich]

Thanks, but the injection pump in my car has only one solenoid on the back end.

[Tom Colitt]

I agree with Joe and it sounds likely that your injection pump has been replaced with an incorrect pump at some point. In my experience, which is a lot, but still less than Joe's enormous experience, on a 1968, that switch was used to change the fuel delivery to zero, in coasting conditions, depending on load, via throttle position and engine temperature on US spec cars, mainly to reduce emissions. The switch was part of a separate wiring harness that was taped up along with the main engine harness and you can use the same wiring diagram that is covered in the BBB in the emissions section, but if you don't have the second injection pump solenoid, then that whole system is not operational anyway...

[zdzich]

Thank you Tom. Right now the car is in a paint shop and when i get it back I'm gonna take a close look at the injection pump. Unfortunately, I don't have the BBB. I'm still looking for a wiring diagram for this car. The only book I have is the Haynes repair manual for 230 250 and 280 SL. I noticed that the W108 with the 129.980 engine that I have was only made in 1967-1968. In this book there is only some information that I found useful for my car. Unfortunately, for early Mercedes cars there is not a lot of information available anymore. Do you know where I could download, if available, any service manual with wiring diagrams for this car ?

[66andBlue]

The service manuals for our cars are described here: http://www.sl113.org/wiki/Documents/BBB
They show up on eBay quite often.

[zdzich]

thank you very much, I will try to find one on eBay.

[wwheeler]

Here is the emission wiring diagram. My '68 280SE W111 follows this pretty closley. The switch you are showing is #6.

[zdzich]

Thank you very much WWHEELER !

[glenn]

Coupe or 4 door?  Got a 4 dr here....

[zdzich]

4 door