If the tach only has three connections, the spade that is NOT earth/ground will get a switched 12V supply from the fuse box. Almost any solid green color wire (no second color stripes) can be used to supply the tach. The earth/ground connection needs to be to a good clean spot. The bullet connector is for a wire that runs to the coil (-) terminal (the terminal with the ignition module's black wire).
EDIT: Sorry ! I forgot to say congratulations on getting the engine started!