[Richard L]

This is very strange.

The two wires of the HFS-3:

Red: ............ + reference of a comparator input
Green: ........... - reference of a comparator input

The trigger differential is set to ~0.5V between those two points. Ie is the voltage of green wire is 0.5V below the red wire, the system sees it as a starting point of the injector firing.

From the diagram J67 appears to be the main +12V supply to all the injectors and other devices. So I can safely assume that I can use J67 as a (+) reference for the +12V.

If you can post a larger diagram of the ECU that has p60 included so I can see what else is connected to that pin.