Speedometer cable

[Klaus Fluoride]

Hello everyone

Where does the speedometer/tachometer cable insert into the transmission?
I spent yesterday claustrophobically underneath the car (no jack stands) trying to find the cable to disconnect it so I could get to a beeper thats been attached to my indicators in the instrument cluster and driving me insane.

The Haynes manual says it's on the left side of the transmission. I'm pretty sure I found the two cables together in a sheath but there was no way I could see the 10mm nut the manual says connects it. All I could find was what looked like a black rectangle type thing, what's that?

Alternatively, I read somewhere on this site that you can disconnect the speedo by getting access through the speaker cavity on the dashboard, how much easier is that?

Klaus Fluoride
1987 230E