Electric speedometer? Need the experts on this one:)

[2002jm]

I received a cluster yesterday and the speedometer is electric. Well my m535 has a cable driven speedometer, as most of you know...it is an e12.
But here is the mystery. Behind my cluster I found a black box with a bunch of wires coming out including two that were cut....one is black and one is yellow.
The strange part is the back of the electric speedometer has a yellow wire and you guessed it...a black wire.
Is there a chance I can hook up the wires and the electric speedometer will work in my e12? Anyone ever heard of someone doing this?
thanks for any help,
jm

[Falkenberg]

For an electric speedometer you would need an impulse generator located somewhere on your car. I think on E28s it is on / near the differential. Without something like that, it won't work, no matter how many wires you have under your dash.

[2002jm]

I have been reading about these clusters, and have a feeling you are correct.
Did not want to hear that:). Wonder what these wires go to????
Sure is funny they are the exact same color.
jm