So I accidentally hooked up Pin 2 of C104 to the tac signal output of the DME. How did my DME not let the smoke out and die from that? 
Did I just get lucky? I looked at the diagram and it looks like C104 is hot when start. Once I got it all hooked up right all is well and the tach works.
Did I just get lucky? I looked at the diagram and it looks like C104 is hot when start. Once I got it all hooked up right all is well and the tach works.