There are two wires in the loom....real heavy gauge....matching connectors....the tach goes between these wires....same connectors...

If you take the tach out, you connect the two wires in the loom together...put the tach in, and the two wires go to the tach.

I have a tach that I no longer need (doing an SBC swap)....$10 + shipping and it's yours....You can also buy a new one from Krage....I think it is about $50 or so.