I'm not sure what the accessory connection is for. Maybe some future upgrades? With the battery hooked up you can use your home PC to download maps. I haven't finished reading the instructions yet. My Stage 2 is map 1. Before I put it in my car, I hooked it up to my PC to be sure that Stage 2 was on it. The maps are supposed to be available on the TXS web site any time now. They also have dyno plots up for the Utec Stage 1 and Stage 2.