Here is what's happening.
The EI units are edge triggered, either positive or negative slope. Anyone who designs a trigger system that is not edged triggered must have a very, very specific reason for doing so. The input is usually differentiated or the input looks at the rate of change (positive or negative) of the input waveform.
The Bosch trigger unit uses a magnet in the stator (the stamped metal part that is mounted on the advance plate) and the rotor is mounted on the dizzy shaft (or the part that rotates with at cam speed).
The edge of the output pulse occurs as the edge of the rotor crosses the lines of flux in the stator.
Reversing the wires or reversing the direction of rotation will cause the edge of the waveform to occur at the trailing edge of the rotor.
The actual amount of error is small, a few degrees of ignition timing and since this is a fixed error, it nulls out once static timing is set. Above 4,000 RPM when all the mechanical advance is done, it makes even less difference.
Try this experiment since you have a "scope".
These images are taken with a Bosch dizzy used in the X1/9 driven by a cordless drill and a Tektronix 2467 micro channel plate portable O'scope (Yes, it analog and I prefer them for stuff like this)
Here is the same waveform posted, dizzy driven in the same direction as the FIAT engine turns, slope trigger set to positive.
The dizzy trigger coil leads can be reversed or dizzy rotation reversed and the same display will result. This is due to the scopes trigger circuit only responding to a positive going slope, just like the Bosch or MSD or etc electronic ignition unit.
Same waveform enlarged, note the jitter at on the right hand end of the trace, this is due to the speed instability of the cordless drill:
Now we flip the scope trigger slope to negative and we get this:
Same waveform enlarged.
Does it matter what the polarity or phasing of the trigger pick up coil is, yes, But it does change the static timing by a few degrees or the width of the stator/rotor fingers which nulls out once static timing is set.
If there is mis-triggering, the problem is more likely to be in wiring dress or physical location of the magnetic pick up wires. These wires must be run as a parallel pair together and kept away from any other wires that produce large magnetic fields (like power cables or far worst the wires that drive the ignition coil). If this is not done, mis-triggering can and will happen.
Bernice
You're partially correct. The brown and green wires that go to the dizzy do trigger the CD unit and allow the coil to charge and discharge, but there is polarity, and how the magnetic pickup is wired will affect ignition timing.
If polarity is reversed the CD unit will act on the wrong part of the waveform generated by the pickup and igntion timing will be erratic. I scoped this asymetrical wave (shown below) to show this. The mostly vertical spikes are produced when the trigger wheel lines up with the poles, and the downward slope is caused by the time in between the poles(below is a distributor showing trigger wheel and poles(911turbo but concept is the same)). The CD unit acts on the signal when the wheel lines up with the poles. If polarity were to be reversed, the CD unit would act on the time in between the poles or on the downward slope which is not as defined which leads to varying or erratic timing and can be verified with a timing light. If this were a symetrical wave polarity would not mater.
