[Dangerous Doug]

I am using a harness ground. Admittedly, when I first wired it six months ago I hadn't grounded it correctly (neg needs to be tied to ground). I think with the floating ground it may have damaged the circuitry and now reads incorrectly.

I've already purchased a new tach, so I'll put that in, test it. I'll check the ground again in the process, as well as the +12V. Beyond that, I guess I may be playing with better shielded spark plug wires...

DD