Tachometer pickup?

[Maxwell]

My car has no tach in the instrument cluster but it does have what appears to be a tachometer pickup, my question is, why is that there? is it part of the cruise control? did my car originally have a tach? could the pickup i have be hooked up to a tachometer? It is a cylindrical thing above the harmonic balancer with a wire leading back to the left fender wall where there is a big cylindrical plug to the rest of the wire which joins the mass of wires going through the firewall, there is nothing that fits the description of the tach amp, but it seems like this must be a tachometer pickup.