Loose nut

[mbz.280sl]

OK this is not a joke. I recently had the speedometer, tachometer and gauges taken out for repair.
The shop did a great job and everything is working perfectly after the repair and re installation.
While driving a couple of weeks ago I found this loose nut under my feet on the drivers side.
I believe it's a 7/16 size nut. I don't think it is from the speedo, tach or gauges.
Can anyone tell me where this belongs?
I have a 1969 280 SL 4 four speed.

Thanks,

[Naj ✝︎]

Pedalbox?

[stickandrudderman]

The bin?

[waltklatt]

Uh Oh, better stop driving.
That nut looks to be the thin narrow one that locks the brake pedal adjuster bolt for the connection between the booster outrigger and the pedal.
Look under the dash and look for the brake pedal linkage and where it meets the prongs for the booster outrigger.
There is a longish black bolt there.  Should also have a washer that looks like a roller coaster wave.
Walter
1967 220SL-diesel

[mbz.280sl]

Thank you Walter.
My car is safely stored away in a garage right now.
I'll check this out this week.
Thanks again,

[mbz.280sl]

I checked under the dash to see where this nut should be attached but had no luck finding what was described by Walter.
Everything under the dash for the brake pedal is secure.
But in the process of looking I discovered a loose cable or wire hanging down (picture attached).
Everything in the dash is working - tach - Speedo - all gauges - radio - cigarette lighter - clock.
So what is this cable with the covering that slides over the end and the spring on the end?

Thanks in advance for the help.

[66andBlue]

Looks to me like one half of a fuse holder.
Could have been used for radio, or antenna, or A/C ?

[w113dude]

It could be a loose nut that was lost under the dash that just fell, I have found many washers and screws wedged in various tight spots.