What is the little electronic device for ?

[andrew.lori]

I have a couple instrument assemblies and I just discovered there is a difference with the Speedos???
If you look at the picture you will see a little electronic box added to one of the speedos and it is OEM.
What the heck is it for.
I plan to list both assemblies in the classified but would like to know what this is before I list.
Thanks
Andrew

[RMS]

must be a 73 thing? I have a stack of clusters and not one has that box.

[bertvorgon]

If I can contort myself enough to look up under my dash, I will take a look and see if there is one on mine...I do not remember.

[datzenmike]

The rusty box? I think it's a speed switch probably for emissions. Notice that one speedo stops or starts at 10 MPH and the other at Zero? My B-210 had something like this. When the needle touches the 10MPH it opens a switch I think.

On deceleration my B-210 had a very slight fast idle. As you slow in first gear the speedometer touched 10MPH the engine would lurch down to it's set idle speed. Perhaps a rudimentary BCDD to lower emissions.