I'm installing an 8K Autometer Monster Tach I got off ebay. I got sick of the stock tach bouncing between 0 and 4k RPM. While wiring it up I ran into a little uncertainty.

Presently I have the negative pertronix output connected to the Megasquirt tach input (with 1.3K pulldown resistor). Then I have the megasquirt triggering the negative side of the coil. The stock tach was hooked up to the negative side of the coil as well, worked fine.

I came across the following warning in the installation manual for the tach:

"Warranty will be void if connected to coil when using an aftermarket ignition box such as, but not limited to... MSD, Crane, Jacobs, Mallory, Holley, etc.."

Am I safe connecting the tach to the negative side of the coil. The Megasquirt is triggering the negative side of the coil. Come to think of it, shouldn't really matter. Previously the pertronix (or points) were used to trigger the negative side of the coil.

Any suggestions? I think the warning is for high power output system. Not sure..

the ignition boxes they warn about.... because those send amplified voltage to the coil.... which fries tachs, test equipment, etc.... (just ask rhodyguy )

you should be fine if the MS is just sending a trigger signal vs a capacitive discharge ignition (CDI) amplified voltage