Help! How do I hook up this tach?

[scottveazie]

Hey guys, I've had this spare OMC (Stewart Warner) tach sitting around for a few years, and I thought it would fit nicely in my '65. The problem is, I can't figure out the correct procedure to get it working. As you can see, it has on spade terminal on the back, and two screw terminals. I tried running the neg. off the coil to the spade, and pos. to the screw terminal, and it kills my engine. It's a 4-6-8 cylinder tach and I've got it on 8, but I can get it to register. Any ideas?

Also, the sweep of the tach is greater than the opening of the cluster, is there a way to open that up on the cluster and have it still look good? I can remove the plastic binnacle and window on this tach easy btw. Thanks!