I did this swap on a friend of mines car when we did it we changed out the engine harness along with the engine didn't have any problems starting it up so it maybe the harness, however I'm not an expert.

 

I did that. The main harness is from the car the motor came from. The drivers side harness is from the car. i need to know what that wire does.

 

Looks like the oil pressure sensor wire to me.

 

that keep it from starting? I did the unflood, put some oil in the chamber. The whole shabang. Changed the ECU. I know it isnt anything serious. I guess next i need to check for spark..

 

Nah, that wire shouldn't keep it from starting. If it's flooded, then when you try to start it, it will smell like gas - if that's happening, then when you do the unflood, keep cranking until it starts and dies right away, then you should be unflooded enough to plug everything back in and start it.

Otherwise, you're looking at a different issue.