Stewart Warner tach problem

[lippy]

My first start and drive of ERA 797 have gone surprisingly well. But the two outstanding items I have are a non-operatational tach and speedo.

The SW tachs are supposed to work with the MSD ignition modules without the MSD adapter you need for some of the tachs. I used a digital Fluke meter set to DCV and measured the tach output wires at the connector under the hood, and at the tach itself. I get the same results: power = 14v, trigger = approx. 7v. I understand the trigger is a 12v square wave with a 25 degree duty cycle, so that is why I may be getting a different trigger reading. But I do appear to have adequate voltage for both connections - neither are zero. I have a hard time believing the tach is dead and usually default to assuming that I screwed something up (an assumption that mostly is correct).

Any idea what might be the issue, or if there is anything else I could check?

[patrickt]

... separate the tach wires as specified here? MSD Installation

[lippy]

Originally Posted by patrickt

... separate the tach wires as specified here? MSD Installation

Good point, but yes, I did. Thanks.

[lippy]

I ran an external, temporary ground to the tach and that did it, so now I know where the problem lies.