obd II install?

[crustysack]

installing an 02 ls1 into a 65 GTO,I have a 5 wire obd II port -can someone tell me where these wires should go- I know 1 is the data from the computer and there are 2 grounds- what is the difference between signal ground and chassis ground?? 1 is power from the battery (+ constant) what is the last wire for??? any help greatly appreciated- will try and post a pic of it later thanks