OK, here is what I know so far. First, what I said about the diagnostic port.... forget that, its nothing to do with it. This is the short harness for the k5 with the immobiliser, I'm assuming yours isn't a North American model which don't have them.
This goes in to the harness between the ignition switch and the main harness. As you can see it has 2 wires only. Red = 12v in to switch, orange = 12v switched from switch. The reason the turn signals and brake light won't work is because the other 2 wires going in and out of the switch (grey 12v in, brown 12v switched out) are the wires that power that circuit.
Now, heres the interesting bit. I sat here for over an hour looking at the harness and the wiring diagram and I can't see any reason it won't work. You must disconnect the immobiliser at the black plug, so the Yosh paperwork that came with the short harness says, or the motor won't run.
If you have a workshop manual you can check for yourself. Look at the ignition switch, then follow the grey and the brown wires and see where they go. I can't see them going anywhere near anything that effects the ECU.
Hope this helps, miller.
Did you know that if you have the race wire harness you can use the left switchblock to change maps and activate the pitlane speed limiter. If the EM Pro does work we may be able to figure a way to make these funtions work with the standard harness.