webber carb on 258 cj7
10-12 gauge wires? Those are some big wires for a tach, usually they only run a 18 guage at the most. most after markets are 20 guage. A tach is pretty simple to wire up. just need to be sure about what you got. The most basic tach will have nothing more than a threaded adaper that looks a lot like a speedo attachment but smaller, these are the old mechanical tachs, the most simplest electric tach would have two wires, one to receive the signal from the coil and one to revieve 12 volts. the tach would have to be mounted on metal cause it uses this as a ground. These were common in vehicles with metal dashes (early 60's GMC's with factory tach option) or some vehicles that had them on the hood. this sounds like what you got. I am not too sure if the CJ tach was like this though. CJ's had metal dashes right.
