I just want to know what wiring is absolutely necessary to make the car start up. Not anything like break lights, power windows, gauges. Just to connect the engine to the ecu and what else to make it start?

 

bump

 

Well,

It stands to reason that if its in the ECU harness, its required to make the engine go.

 

so what about the rear harness that connects to the fuel pump?

can i just wire the fuel pump to a switch?

 

If you are feeling particularly suicidal, you can hardwire the pump to a switch. But in that harness, there is your fuel level signal..

 

maybe you should post the problem you are having, or goal you are shooting for... it would be much easier to help that way

you absolutely need:
ecu harness
right side engine harness
dash harness
rear harness or rewire fuel pump

of course, if you wanted to, you could rewire everything but the ecu harness and leave out all the non-engine parts.