I've tried in the past to build cables to get it to work, so this time I decided to build the circuit on a breadboard first, and use the cigar lighter as the power supply. And it worked! I turned on the car and it started receiving data. Looking at the TPS signal, I could press the throttle and see the results onscreen. I didn't use a 10kOhm resistor between terminals A & B in order to get the unaltered data.
Used a Thinkpad X24 with the X2 ultrabase for it's serial port. The computer fits perfectly into the seat indentation.