Before getting into an install example, let's look at a distributor with a Crane Optical Trigger wheel. The diagram below applies to a Crane Trigger wheel, but illustrates other Optical or Hall sensors as well. The diagram is conceptual only and does not show construction of the optical shutter or electrical connnections. See individual installs for the correct wiring.

 

In this type of configuration the light from the LED reaches the Pick-Up during the smaller gap. Your Sensor may be different. The transition from no light at pick-up to full light is the Trigger Angle. When the distributor is used without MegaSquirt, this position is usually near 10º BTDC. This works fine for Next Cylinder mode. In order to use This Cylinder mode, the Opto Trigger will have to be moved about 50º counter clock wise (against the rotation of the trigger disc). Moving the distributor will accomplish this as well, but will also change the position of the HV towers relative to the crank TDC. Not a good thing. This makes installing This Cylinder mode more complex than Next Cylinder mode. For optimum performance with the Crane Trigger assembly, the angle of the gap (between Trigger Angle and Trigger Return) must be increased to use Trigger Return.