Switch for constant speed solenoid

[frostpinfold]

My car is 1969 280 sl with automatic transmission. US spec but no emission items.
I have spent hours looking at the wiring diagrams in my Haynes manual and on this website but cannot find information about the switch which controls the solenoid that increases the engine speed when the gear is engaged in the automatic transmission.  The only diagrams I can find show the solenoid being activated by the A/C (if fitted which doesnt apply to my car)
There is a firewall mounted switch which is activated by a cable from the speed selector. I assume this is relevant to my problem but is not shown on any diagram I can find.
Does anyone have information as to how to test the switch and where the wires are supposed to go?

Rob

[WRe]

Hi,
the constant speed solenoid (6) in our cars with automatic transmission (w/o AC or US ECS) is operated by 2 oil pressure switches (forward 7 and reverse 8 ) by switching ground to the solenoid. Attached a diagram of connections.
...WRe

[Pawel66]

You have quite a lot of it in the Technical Manual here. But take the enclosed diagram form WRe, not the one that is there.

[wwheeler]

Is the firewall switch you are referring to triggered by the throttle shaft that runs along the firewall? If so, that is a microswitch and related to the US emissions fuel shut off system. If you have two solenoids on your Injection pump, the larger and lower solenoid is the fuel shut off solenoid. That has nothing to do with the CSS that increases idle speed.

The pressure switch you are looking for is #001 542 13 17 and there are two as WRe has said. They are connected together by a cloth wire that runs over the transmission. Then another wire that runs to the solenoid that provides the ground. Over time, the switches do fail.

What exactly is your issue? The solenoid doesn't work? Easy to test the switches by putting the trans in gear (rev or drive) and see if there is continuity between a ground and the pressure switch.

[frostpinfold]

Thank you for the response
Thats very helpful and very obvious once you realise how it works
Why I cant find a correct wiring diagram for my car I dont know

Rob

[Pawel66]

Some of the parts of wiring are to be found only in BBB (Big Blue Book), the workshop manual and on this forum.