When the ignition switch is turned on fuel injector negative turns to positive?

This happens when the fuel injector is not getting power or the PCM is shorted out. I would check all fuses and grounds to start. Also, the fuel injectors get their power from the TPS sensor. Here are the engine and fuel injector wiring diagrams so you can see how the system works and which fuses to check. This guide can help you:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the images (below). Please let us know how it goes.