Kakashi

I've searched everywhere but couldnt find any kind of diagram about how to do this. I tried wiring the harness directly to the stock harness color for color but end up with extra wires. Everything works except the gas gauge and the check engine light stays on. I know this has been done before but I cant seem to find any answer on how to do it. If someone could direct me to some kind of diagram or know which wires go where I would appreciate that. Thanks.