Doing Gsr swap in my ls using a gsr wiring harness obd2. On the passenger side shock tower harness connectors all fit except for this forth connector, wondering what's it for. Also for vtec to engage do I need to wire the vtec solenoid to the p72 ecu even though I'm using a Gsr wiring harness or should everything be plug and play since I'm using a gsr wiring harness and p72 ecu.

 

What are the wire colors for the three wires in the plug you are holding ?

 

Found out it's a evap plug

 

But for vtec to engage do I still need to wire vtec to the ecu p72 obd2a even though I'm using the gsr harness obd2a.

 

You will still need to wire VTEC to the ECU even if you have a GSR harness. The LS is missing those plugs for VTEC, IAB. Its why I went back to my LS harness+subharness for VTEC vs running the GSR harness on my car.

 

Identify the VTS, VTP, Knock, and IAB wires on the GSR engine harness. They will likely be green/yellow, blue/black, red/blue, and pink/blue respectively. Follow them back to where the engine harness plugs into the chassis harness and then examine the chassis side plug to make sure there is a corresponding wire on that side that would connect to the needed wires discussed previously. What you should find is that these positions on the plug will be empty and have a weatherproof sealing plug in the hole instead. You can then run wires between the ECU and the chassis harness/engine harness junction and pin them to the appropriate corresponding wire location and ECU plug position.