I use an Auto Meter tach in my ITS RX-7. These tachs are set up for 8-cylinder engines; for others, you clip a wire or two. When I installed the tach, someone told me to clip the brown wire (which is what you do for most 6-cylinder engines).

I did so, and the tach reads funky. Basically, it indicates about two-thirds of my actual RPMs.

I put in a call to Auto Meter on this, but I had to leave a message and they're taking their own sweet time getting back to me. Anybody know which wire(s) I should clip?