Well, that will be your problem... Always connect all the 3 wires to the diagnostics port. You could have had it working yesterday, when you (probably) used the power supply of the same computer as to where the RS232-interface was connected to (since in that case the ground of the power-connector was used), but this isn't the proper way of doing things and you'll be creating a "Ground-loop"... Greetz, Peter. Can i use the black cable on the ttl-232r-3v3 usb cable for ground? Or should i find a real ground and connect to there? TIA doooda