Well obviously everyone spaced on it and only thought about the power supply not the grounds. Power supply wont change except for the eccs relay that supplies power to possibly that pin depending on which 12v switched it is as there are 3 on the ecu, 1 permanent 12v and several grounds so yeah. You wouldnt have seen your 12v switched if it was on the pin that is supplied from the eccs relay as the relay wouldnt have grounded. lol.
Either way, easy thing to overlook. Should work just fine once you ground those grounds on the engine harness.