[turboguzzi]

following my transmission swap was casually checking around the engine and all of the sudden i see a disconnected connector coming from top of the gearbox case.
I remembered connecting the three connectors as per the manual: reverse, 4H and 4L to their sockets, all these lights work, what could it be?

well, followed with my hand the disconnected wire, and surprise surprise, it leads to a second switch, just next to the reverse switch... see first pic. it's the darker one further down the transmission tunnel. went through all the manuals in my library, none of them mentions a second switch screwed to the top of the gearbox, neither do the wiring diagrams show another gearbox switch.
second pic is of my original gearbox, you can clearly see there is a dimple that is left unused, but thats where the mistery switch in my car is installed.
car runs good, all systems work as they should, so no biggie, just a mistery
in case it helps, you can see the gearbox serial number, but all that "M" tells me is that it's from a 1991 car.
your ideas of what is it for are welcome,

 

[fordem]

See if it closes in 5th gear.

 

[turboguzzi]

looks like you are right, found it now in an EFI model list, so it sends a signal to the ECU to do something different in 5th?

 

[fordem]

I think it has something to do with enabling/disabling EGR.

 

[Bex]

It disables the EGR in 5th. I don‘t know if it has other functions.