well im tring to intigrate the ls1 harness into my factory one ,the ecm and all the engine wires are out and i have located the coolant ,tach . oil wires all the powers ont the factory side and most on the ls1 . im wondering if anyone has done this before and i just want to check exactly what wires need to be powerd ,also need to know what wires i need to pull out for the data link for the obd 2 plug . my other question is when i pulled the motor and ecm i turned the ignition on to see if the dash still worked and everything works except the mileage dosnt show up on the digital dash dose that run through the ecm or is ther just a gound it needs to run through.

 

The mileage is stored in the PCM. Check out ls1tech.com for wiring tips in the hybird section.

 

LS1 harness vary by year, and you didn't specify what year yours is.

Power to the LS1 harness isn't the only concern in a transplant...you also need to get power to the 3rd gen chassis, gauge feeds from the LS1 to the chassis, control the cooling fans, control the fuel pump relay, get data to the OBD-2 connector as you mentioned, control the Check Engine light, etc.

You're basically asking for someone to type up their Helms manual for you.