OK, I got the multimeter out, and here we go...
My test procedure: I created a jumper harness to go between the connections on my current harness. There are staggered bare spots on the wires, allowing for safe, short-resistant voltage measurements. What's next? All measurements with the coil attached, key ON, engine OFF:
Ignition signal, no PP: 1.2 mV
Ignition signal, w/PP, before PP: 104mV
Ignition signal, w/PP, after PP: 7.4V
This explains things... In this state, the ignition signal is supposed to be 0V. With the engine running, the signal is supposed to be 1-3.4V. How did it get to 7.4V?
EDIT: I just came across this gem:
This would lead me to believe that, when sending 104mV in, the output should match that. Something is amiss! (9/15/06)
At RPM position zero (bottom map row) the output signal is copied from the input, and no timing is applied. This allows the changing of input and output polarity, until the engine starts and runs. At this point the RPM indication should be correct. (DM, p.22)