Below is the wiring for the Unitlite optical trigger
driving the MegaSquirt ECU. Add a 470 ohm 1 watt resistor to +12 as
shown. Alternately add the 470 ohm resistor internally to MegaSquirt
at +12V and to Optoin. Make all the green jumper connections
as shown.

You can test your input connection by monitoring IRQ-1
at R13. First set up MS to monitor IRQ with the center front panel LED.
Disconnect power to the coil. Put on the hand brake and the car in neutral.
Now turn the engine such that the crank pulley passes from 20º
BTDC to TDC. The IRQ LED should go from On to OFF at ~10º BTDC
for most cars with distributor (but it may be from 5º to 15º,
usually this is called the static timing)
The MegaSquirt will in turn then drive a single
external coil.