The tach signal is an output from "the ignition box". So...disconnecting the tach does nothing UNLESS the traction control is IN the tach? I'd be looking for "extra" wires (probably hidden in braided lines) to the bellhousing/transmission/differential/rear axle hub area for speed sensors. I supposed, given technologies progress, might be able to detect RPM change thru vibration?Some think the traction control units are controlled by the engine RPM's. Unhook the tachs, TC doesn't work.