help please
 

I have an 87 supra and under the hood theres a green wire hanging off and now the car wont start unless some1 is in the car turning the ignition and some1 else is under the hood and they have to keep touching the green wire to the battery but u cant keep the wire on it and i dont know where the green wire is supposed to go i dont know if its the hot wire or what could some1 please tell me what it is and where its supposed to go