You trace back on the diagram. The light green/red wire doesn’t go straight to the ECU. It goes through a little black box near the strut tower: .
It’s your Rosetta Stone. You spread the printout over the fender, holding the edges down with a 10mm socket (the one you haven’t lost yet) and a half-empty bottle of water. The diagram is a labyrinth: lines crossing lines, little numbers in circles, connector shapes that look like someone sneezed while drafting. There’s for engine room main junction, E for earth points, I for instrument cluster. Toyota Starlet Ep91 Wiring Diagram
You start tracing.