How do you wire a factory tach?

[flyin99]

I bought a dash cluster with tach. and a wiring harness, but I am lost here.......back of tach. has 2 male terminals pointing down and a threaded terminal in between the 2.the harness has a female plug, but it is shaped sort of like a V or something and a single red wire with some kind of piggy back on it....the other end has a wire coming from the V shaped plug going to a grommet, like it goes through the firewall somewhere.............any ideas? Thanks