Code P0201, occasionally going into limp mode when driving, could it be the fuel injectors?

Hi. My wife's vehicle occasionally goes into limp mode when driving long distances. I've since scanned the car and p0201 fault. Injector #1 circuit open/shorted. I've carried out numerous tests, and found a high voltage drop on injector feed wire. There is only 1. 2 volts on injector feed wire rising to 5v with engine running. I've stripped the wire harness down looking for a partial break or corrosion and found nothing. The only thing I did find was the wire braid on the starter motor was badly corroded and frade. I've since had that repaired and will connect it back up tomorrow. Not sure if that's going to solve the problem. If it doesn't, I'm at a dead end without a wiring diagram for the fuel injector circuit. I also carried out all testing with the injectors unplugged and tested the injectors as well. Injectors are with spec. I've got 1.2 v with injectors unplugged and I also unplugged the wire harness that supplies power to injectors and glow plugs. I'm also getting 1.2v at that multi plug as well so the problem is before that. Can anyone help?