If you have the original harness and its wired into the Lamps circuit in the fuse box, than with the tach you have you'll have to pull the headlight switch for the lights to come on AND for the needle to move. It seems you have the correct readings, if you have power with the engine running, ground is good (verify with Amp meter) and you are connected to the coil and you pull the light switch the tach should work. The Parts p[lace, mildly put is not one of my favorite suppliers, they offer 2 tach styles, 1 was made in 2007, the others are new, and they are still selling both styles. You can see on the tag when yours was made. The newer one has better electronics and the older one may need a tap to free up the needle.