Nah what I meant is the actual ALDL communication line, This line run at 4.4 - 5 volts. For VN/VP's, the comms line is on the CEL ( Check engine light) line and is at 12volts.. sooo I would have thought we would see some smoke popping out of a standard aldl cable without some level conversion/resistors! Unless the chip has internal resistors ect but I wouldnt want to be stressing them anyways.Most of the cables main chip is low voltage, should have a 5v reg in the circuit somewhere (some circuits I've seen iirc are powerd from the pc not the car)
But yeah you are right, there are some devices that run off the cars or computers power. I feel the PC's output is a bit more reliable/stable due to a cars output is quite noise which could reflect in a 5v regulators output if its all over the place.
Anyway for anyone interested, see here for reference: Techedge